Implement mediaGalleriesPrivate api to notify extensions about gallery changed events.

chrome/common/extensions/api/media_galleries_private.idl

Index: chrome/common/extensions/api/media_galleries_private.idl
diff --git a/chrome/common/extensions/api/media_galleries_private.idl b/chrome/common/extensions/api/media_galleries_private.idl
index 5b8b2f4ce11a0e1b3c3e0ac079f743c2244a2b98..b3c7f4970a74a09548db7ae05d3ab0c28fb46340 100644
--- a/chrome/common/extensions/api/media_galleries_private.idl
+++ b/chrome/common/extensions/api/media_galleries_private.idl
@@ -21,11 +21,34 @@ namespace mediaGalleriesPrivate {
     DOMString deviceId;
   };
 
+  // A dictionary that describes the modified gallery.
+  [inline_doc] dictionary GalleryChangeDetails {
+    // Gallery identifier.
+    long galleryId;
+  };
+
   interface Events {
     // Fired when a media device gets attached.
     static void onDeviceAttached(DeviceAttachmentDetails details);
 
     // Fired when a media device gets detached.
     static void onDeviceDetached(DeviceDetachmentDetails details);
+
+    // Fired when a media gallery is changed.
+    static void onGalleryChanged(GalleryChangeDetails details);
+  };
+
+  // A dictionary that describes the add gallery watch request results.
+  dictionary AddGalleryWatchResult {
+    long galleryId;
+    boolean success;
+  };
+
+  callback AddGalleryWatchCallback = void (AddGalleryWatchResult result);
+
+  interface Functions {
+    static void addGalleryWatch(long galleryId,
+                                AddGalleryWatchCallback callback);
+    static void removeGalleryWatch(long galleryId);
   };
 };