[Blink>MediaSession] Use setActionCallback() instead of event listeners for media control actions

third_party/WebKit/Source/modules/mediasession/MediaSession.idl

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://wicg.github.io/mediasession/#enumdef-mediasessionplaybackstate
 
 enum MediaSessionPlaybackState {
     "none",
     "paused",
     "playing"
 };
 
 // https://wicg.github.io/mediasession/#the-mediasession-interface
 
+enum MediaSessionAction {
+  "play",
+  "pause",
+  "playpause",

[mlamouri (slow - plz ping), 2016/12/20 13:25:57]

playpause is no longer there, right?

[Zhiqiang Zhang (Slow), 2016/12/20 13:53:06]

Thanks for the catch. Done :)

+  "previoustrack",
+  "nexttrack",
+  "seekbackward",
+  "seekforward"
+};
+
+callback MediaSessionActionCallback = void ();
+
 [
+    Custom=VisitDOMWrapper,
     RuntimeEnabled=MediaSession,
 ] interface MediaSession : EventTarget {
     attribute MediaMetadata? metadata;
-
     attribute MediaSessionPlaybackState playbackState;
 
-    attribute EventHandler onplay;
-    attribute EventHandler onpause;
-    attribute EventHandler onprevioustrack;
-    attribute EventHandler onnexttrack;
-    attribute EventHandler onseekforward;
-    attribute EventHandler onseekbackward;
+    // Why `MediaSessionActionCallback?` will generate bindings with `Nullable<MediaSessionActionCallback*>` instead of `MediaSessionActionCallback*`?

[Zhiqiang Zhang (Slow), 2016/12/19 21:21:08]

bashi@, do you have answer to this question? If I use VoidCallback, the
generated binding will use `VoidCallback*`.

[bashi, 2016/12/20 06:02:10]

That seems a bug in the code generator. Thank you for reaching out to me. I'll
upload a fix.

+    void setActionCallback(MediaSessionAction action, MediaSessionActionCallback callback);

[mlamouri (slow - plz ping), 2016/12/20 13:25:58]

I would prefer to keep Handler to match the discussion on the spec issue. We can
always change this later if needed.

[Zhiqiang Zhang (Slow), 2016/12/20 13:53:06]

Done.

 };