Bug 1595860 add a utility function to map pref names to extension settings r=robwu

Differential Revision: https://phabricator.services.mozilla.com/D57909

--HG--
extra : moz-landing-system : lando

toolkit/components/extensions/ExtensionPreferencesManager.jsm

@@ -234,6 +234,29 @@ this.ExtensionPreferencesManager = {
     return defaultPreferences.get(prefName);
   },
 
+  /**
+   * Returns a map of prefName to setting Name for use in about:config, about:preferences or
+   * other areas of Firefox that need to know whether a specific pref is controlled by an
+   * extension.
+   *
+   * Given a prefName, you can get the settingName.  Call EPM.getSetting(settingName) to
+   * get the details of the setting, including which id if any is in control of the
+   * setting.
+   *
+   * @returns {Promise}
+   *          Resolves to a Map of prefName->settingName
+   */
+  async getManagedPrefDetails() {
+    await Management.asyncLoadSettingsModules();
+    let prefs = new Map();
+    settingsMap.forEach((setting, name) => {
+      for (let prefName of setting.prefNames) {
+        prefs.set(prefName, name);
+      }
+    });
+    return prefs;
+  },
+
   /**
    * Indicates that an extension would like to change the value of a previously
    * defined setting.

toolkit/components/extensions/test/xpcshell/test_ext_extensionPreferencesManager.js

@@ -869,3 +869,19 @@ add_task(async function test_preference_select() {
   await three.unload();
   await promiseShutdownManager();
 });
+
+add_task(async function test_preference_select() {
+  let prefNames = await ExtensionPreferencesManager.getManagedPrefDetails();
+  // Just check a subset of settings that are in this test file.
+  Assert.ok(prefNames.size > 0, "some prefs exist");
+  for (let settingName in SETTINGS) {
+    let setting = SETTINGS[settingName];
+    for (let prefName of setting.prefNames) {
+      Assert.equal(
+        prefNames.get(prefName),
+        settingName,
+        "setting retrieved prefNames"
+      );
+    }
+  }
+});