Bug 1276272 - part 2 - modify the webidl and preference setting; r=ehsan

MozReview-Commit-ID: INYkaXhe8gT

--HG--
extra : rebase_source : ee6029f930e8ee9bb4d8f9576faea8f827b2aae4

dom/webidl/HTMLMediaElement.webidl

@@ -212,7 +212,5 @@ partial interface HTMLMediaElement {
  */
 partial interface HTMLMediaElement {
   [Throws, Pref="media.seekToNextFrame.enabled"]
-  void seekToNextFrame(); // This API should be an asynchronous one which
+  Promise<void> seekToNextFrame();
-                          // returns a Promise<void>. Bug 1276272 follows this
-                          // issue.
 };

modules/libpref/init/all.js

@@ -5453,5 +5453,5 @@ pref("media.default_volume", "1.0");
 #ifdef RELEASE_BUILD
 pref("media.seekToNextFrame.enabled", false);
 #else
-pref("media.seekToNextFrame.enabled", false);
+pref("media.seekToNextFrame.enabled", true);
 #endif