Chromium 关闭 Google Chrome 后继续运行后台应用功能分析c++

此功能允许关闭 Google Chrome 后继续运行后台，控制此功能的开关是

// Set to true if background mode is enabled on this browser.

//更改此值可以修改默认开启关闭

inline constexpr char kBackgroundModeEnabled[] = "background_mode.enabled";

chrome\browser\background\background_mode_manager.cc

// static

void BackgroundModeManager::RegisterPrefs(PrefRegistrySimple* registry) {
  
  //更改此值可以修改默认开启关闭
  registry->RegisterBooleanPref(prefs::kBackgroundModeEnabled, true);

}

1、此功能前端代码

chrome\browser\resources\settings\system_page\system_page.html

<if expr="not is_macosx and not chromeos_lacros">
    <settings-toggle-button
        pref="{{prefs.background_mode.enabled}}" //监听prefs变化
        label="$i18n{backgroundAppsLabel}">
    </settings-toggle-button>
    <div class="hr"></div>
</if>

2、c++对应kBackgroundModeEnabled监听实现代码

chrome\browser\background\background_mode_manager.cc

///
//  BackgroundModeManager, public
BackgroundModeManager::BackgroundModeManager(
    const base::CommandLine& command_line,
    ProfileAttributesStorage* profile_storage)
    : profile_storage_(profile_storage), task_runner_(CreateTaskRunner()) {
  // We should never start up if there is no browser process or if we are
  // currently quitting.
  CHECK(g_browser_process);
  CHECK(!browser_shutdown::IsTryingToQuit());

  // Add self as an observer for the ProfileAttributesStorage so we know when
  // profiles are deleted and their names change.
  // This observer is never unregistered because the BackgroundModeManager
  // outlives the profile storage.
  profile_storage_->AddObserver(this);

  // Listen for the background mode preference changing.
  if (g_browser_process->local_state()) {  // Skip for unit tests
    pref_registrar_.Init(g_browser_process->local_state());
    pref_registrar_.Add(
        prefs::kBackgroundModeEnabled, //监听prefs变化，控制功能开启关闭
        base::BindRepeating(
            &BackgroundModeManager::OnBackgroundModeEnabledPrefChanged,
            base::Unretained(this)));
  }

}

3、允许前端更改prefs值需要加白在

chrome\browser\extensions\api\settings_private\prefs_util.cc

const PrefsUtil::TypedPrefMap& PrefsUtil::GetAllowlistedKeys(){

  // System settings.

  (*s_allowlist)[::prefs::kBackgroundModeEnabled] =

      settings_api::PrefType::kBoolean;

}

=========================================================================

注意：以下是前端更改prefs过程

前端通过chrome.settingsPrivate.setPref接口通过mojom发送给主进程chrome\browser\extensions\api\settings_private\settings_private_api.h接口进行设置。

c++如何定义一个chrome.settingsPrivate接口给前端调用呢？

1、接口定义chrome\common\extensions\api\settings_private.idl

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Use the <code>chrome.settingsPrivate</code> API to get or set preferences
// from the settings UI. Access is restricted to a set of allowed user facing
// preferences.
namespace settingsPrivate {
  enum PrefType { BOOLEAN, NUMBER, STRING, URL, LIST, DICTIONARY };

  enum ControlledBy {
    DEVICE_POLICY,
    USER_POLICY,
    OWNER,
    PRIMARY_USER,
    EXTENSION,

    // Preferences are controlled by the parent of the child user.
    PARENT,

    // Preferences are controlled neither by parent nor the child user.
    // Preference values are hard-coded values and can not be changed.
    CHILD_RESTRICTION
  };

  enum Enforcement {
    // Value cannot be changed by user.
    ENFORCED,
    // Value can be changed, but the administrator recommends a default.
    RECOMMENDED,
    // Value is protected by a code that only parents can access. The logic to
    // require the code is NOT automatically added to a preference using this
    // enforcement. This is only used to display the correct pref indicator.
    PARENT_SUPERVISED
  };

  dictionary PrefObject {
    // The key for the pref.
    DOMString key;

    // The type of the pref (e.g., boolean, string, etc.).
    PrefType type;

    // The current value of the pref.
    any? value;

    // The policy source of the pref; an undefined value means there is no
    // policy.
    ControlledBy? controlledBy;

    // The owner name if controlledBy == OWNER.
    // The primary user name if controlledBy == PRIMARY_USER.
    // The extension name if controlledBy == EXTENSION.
    DOMString? controlledByName;

    // The policy enforcement of the pref; must be specified if controlledBy is
    // also present.
    Enforcement? enforcement;

    // The recommended value if enforcement == RECOMMENDED.
    any? recommendedValue;

    // If enforcement == ENFORCED this optionally specifies preference values
    // that are still available for selection by the user. If set, must contain
    // at least 2 distinct values, as must contain |value| and
    // |recommendedValue| (if present).
    any[]? userSelectableValues;

    // If true, user control of the preference is disabled for reasons unrelated
    // to controlledBy (e.g. no signed-in profile is present). A false value is
    // a no-op.
    boolean? userControlDisabled;

    // The extension ID if controlledBy == EXTENSION.
    DOMString? extensionId;

    // Whether the controlling extension can be disabled if controlledBy ==
    // EXTENSION.
    boolean? extensionCanBeDisabled;
  };

  callback OnPrefSetCallback = void (boolean success);
  callback GetAllPrefsCallback = void (PrefObject[] prefs);
  callback GetPrefCallback = void (PrefObject pref);
  callback GetDefaultZoomCallback = void (double zoom);
  callback SetDefaultZoomCallback = void (boolean success);

  interface Functions {
    // Sets a pref value.
    // |name|: The name of the pref.
    // |value|: The new value of the pref.
    // |pageId|: An optional user metrics identifier.
    // |callback|: The callback for whether the pref was set or not.
    [supportsPromises] static void setPref(DOMString name,
                                           any value,
                                           optional DOMString pageId,
                                           optional OnPrefSetCallback callback);

    // Gets an array of all the prefs.
    [supportsPromises] static void getAllPrefs(GetAllPrefsCallback callback);

    // Gets the value of a specific pref.
    [supportsPromises] static void getPref(DOMString name,
                                           GetPrefCallback callback);

    // Gets the default page zoom factor. Possible values are currently between
    // 0.25 and 5. For a full list, see zoom::kPresetZoomFactors.
    [supportsPromises] static void getDefaultZoom(
        GetDefaultZoomCallback callback);

    // Sets the page zoom factor. Must be less than 0.001 different than a value
    // in zoom::kPresetZoomFactors.
    [supportsPromises] static void setDefaultZoom(
        double zoom,
        optional SetDefaultZoomCallback callback);
  };

  interface Events {
    // Fired when a set of prefs has changed.
    //
    // |prefs| The prefs that changed.
    static void onPrefsChanged(PrefObject[] prefs);
  };
};

2、c++settingsPrivate接口实现

chrome\browser\extensions\api\settings_private\settings_private_api.h

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CHROME_BROWSER_EXTENSIONS_API_SETTINGS_PRIVATE_SETTINGS_PRIVATE_API_H_
#define CHROME_BROWSER_EXTENSIONS_API_SETTINGS_PRIVATE_SETTINGS_PRIVATE_API_H_

#include "extensions/browser/extension_function.h"

namespace extensions {

// Implements the chrome.settingsPrivate.setPref method.
class SettingsPrivateSetPrefFunction : public ExtensionFunction {
 public:
  SettingsPrivateSetPrefFunction() {}

  SettingsPrivateSetPrefFunction(const SettingsPrivateSetPrefFunction&) =
      delete;
  SettingsPrivateSetPrefFunction& operator=(
      const SettingsPrivateSetPrefFunction&) = delete;

  DECLARE_EXTENSION_FUNCTION("settingsPrivate.setPref", SETTINGSPRIVATE_SETPREF)

 protected:
  ~SettingsPrivateSetPrefFunction() override;

  // ExtensionFunction overrides.
  ResponseAction Run() override;
};

// Implements the chrome.settingsPrivate.getAllPrefs method.
class SettingsPrivateGetAllPrefsFunction : public ExtensionFunction {
 public:
  SettingsPrivateGetAllPrefsFunction() {}

  SettingsPrivateGetAllPrefsFunction(
      const SettingsPrivateGetAllPrefsFunction&) = delete;
  SettingsPrivateGetAllPrefsFunction& operator=(
      const SettingsPrivateGetAllPrefsFunction&) = delete;

  DECLARE_EXTENSION_FUNCTION("settingsPrivate.getAllPrefs",
                             SETTINGSPRIVATE_GETALLPREFS)

 protected:
  ~SettingsPrivateGetAllPrefsFunction() override;

  // ExtensionFunction overrides.
  ResponseAction Run() override;
};

// Implements the chrome.settingsPrivate.getPref method.
class SettingsPrivateGetPrefFunction : public ExtensionFunction {
 public:
  SettingsPrivateGetPrefFunction() {}

  SettingsPrivateGetPrefFunction(const SettingsPrivateGetPrefFunction&) =
      delete;
  SettingsPrivateGetPrefFunction& operator=(
      const SettingsPrivateGetPrefFunction&) = delete;

  DECLARE_EXTENSION_FUNCTION("settingsPrivate.getPref", SETTINGSPRIVATE_GETPREF)

 protected:
  ~SettingsPrivateGetPrefFunction() override;

  // ExtensionFunction overrides.
  ResponseAction Run() override;
};

// Implements the chrome.settingsPrivate.getDefaultZoom method.
class SettingsPrivateGetDefaultZoomFunction : public ExtensionFunction {
 public:
  SettingsPrivateGetDefaultZoomFunction() {}

  SettingsPrivateGetDefaultZoomFunction(
      const SettingsPrivateGetDefaultZoomFunction&) = delete;
  SettingsPrivateGetDefaultZoomFunction& operator=(
      const SettingsPrivateGetDefaultZoomFunction&) = delete;

  DECLARE_EXTENSION_FUNCTION("settingsPrivate.getDefaultZoom",
                             SETTINGSPRIVATE_GETDEFAULTZOOMFUNCTION)

 protected:
  ~SettingsPrivateGetDefaultZoomFunction() override;

  // ExtensionFunction overrides.
  ResponseAction Run() override;
};

// Implements the chrome.settingsPrivate.setDefaultZoom method.
class SettingsPrivateSetDefaultZoomFunction : public ExtensionFunction {
 public:
  SettingsPrivateSetDefaultZoomFunction() {}

  SettingsPrivateSetDefaultZoomFunction(
      const SettingsPrivateSetDefaultZoomFunction&) = delete;
  SettingsPrivateSetDefaultZoomFunction& operator=(
      const SettingsPrivateSetDefaultZoomFunction&) = delete;

  DECLARE_EXTENSION_FUNCTION("settingsPrivate.setDefaultZoom",
                             SETTINGSPRIVATE_SETDEFAULTZOOMFUNCTION)

 protected:
  ~SettingsPrivateSetDefaultZoomFunction() override;

  // ExtensionFunction overrides.
  ResponseAction Run() override;
};

}  // namespace extensions

#endif  // CHROME_BROWSER_EXTENSIONS_API_SETTINGS_PRIVATE_SETTINGS_PRIVATE_API_H_

3、在extensions\browser\extension_function_histogram_value.h中定义函数ID

注意extensions\browser\extension_function_histogram_value.h中与chrome\browser\extensions\api\settings_private\settings_private_api.h中类名的对应关系，否则关联失败。//SETTINGSPRIVATE_SETPREF 应是类名(SettingsPrivateSetPrefFunction)去掉Function之后大写！！！！！

4、该类注册在out\Debug\gen\chrome\browser\extensions\api\generated_api_registration.cc

[自动生成的代码，不需要手动添加]

namespace extensions {
namespace api {

// static
void ChromeGeneratedFunctionRegistry::RegisterAll(ExtensionFunctionRegistry* registry)
{   
   {

      &NewExtensionFunction<SettingsPrivateSetPrefFunction>,

      SettingsPrivateSetPrefFunction::static_function_name(),

      SettingsPrivateSetPrefFunction::static_histogram_value(),

    },
  ........................................
}

5、注册api地方 chrome\browser\extensions\chrome_extensions_browser_api_provider.cc

namespace extensions {

ChromeExtensionsBrowserAPIProvider::ChromeExtensionsBrowserAPIProvider() =
    default;
ChromeExtensionsBrowserAPIProvider::~ChromeExtensionsBrowserAPIProvider() =
    default;

void ChromeExtensionsBrowserAPIProvider::RegisterExtensionFunctions(
    ExtensionFunctionRegistry* registry) {
  // Preferences.
  registry->RegisterFunction<GetPreferenceFunction>();
  registry->RegisterFunction<SetPreferenceFunction>();
  registry->RegisterFunction<ClearPreferenceFunction>();

  // Generated APIs from Chrome.
  api::ChromeGeneratedFunctionRegistry::RegisterAll(registry);
}

}  // namespace extensions

6、前端获取prefs实现

base::Value::List SettingsPrivateDelegate::GetAllPrefs() {
  base::Value::List prefs;
  //GetAllowlistedKeys()定义在
  //chrome\browser\extensions\api\settings_private\prefs_util.cc
  //所以要给前端添加新的prefs监听 要在此处加白，否则前端获取不到该prefs值
  const TypedPrefMap& keys = prefs_util_->GetAllowlistedKeys();
  for (const auto& it : keys) {
    if (absl::optional<base::Value::Dict> pref = GetPref(it.first); pref) {
      prefs.Append(std::move(*pref));
    }
  }

  return prefs;
}

7、最后将settings_private.idl 放到chrome\common\extensions\api\api_sources.gni

中，然后进行编译即可。