Hook up RendererMediaSessionManager with browser side

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

Index: third_party/WebKit/Source/modules/mediasession/MediaSession.h
diff --git a/third_party/WebKit/Source/modules/mediasession/MediaSession.h b/third_party/WebKit/Source/modules/mediasession/MediaSession.h
index a10245044e0c75f9c7aab250b1de7ff9dc223fc5..2eee6d11086148e4e9615e0d8596bd2990fc7d5b 100644
--- a/third_party/WebKit/Source/modules/mediasession/MediaSession.h
+++ b/third_party/WebKit/Source/modules/mediasession/MediaSession.h
@@ -7,6 +7,7 @@
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptWrappable.h"
+#include "core/dom/ActiveDOMObject.h"
 #include "modules/ModulesExport.h"
 #include "platform/heap/Handle.h"
 #include "public/platform/modules/mediasession/WebMediaSession.h"
@@ -18,7 +19,8 @@ class ScriptState;
 
 class MODULES_EXPORT MediaSession
     : public GarbageCollectedFinalized<MediaSession>
-    , public ScriptWrappable {
+    , public ScriptWrappable
+    , public ActiveDOMObject {

[mlamouri (slow - plz ping), 2015/12/07 18:14:53]

If you make MediaSession an ActiveDOMObject, you must update the IDL as well.

[davve, 2015/12/08 10:21:23]

Acknowledged.

     DEFINE_WRAPPERTYPEINFO();
 public:
     static MediaSession* create(ExecutionContext*, ExceptionState&);
@@ -26,12 +28,15 @@ public:
     ScriptPromise activate(ScriptState*);
     ScriptPromise deactivate(ScriptState*);
 
+    // ActiveDOMObject functions.
+    bool hasPendingActivity() const override;

[mlamouri (slow - plz ping), 2015/12/07 18:14:53]

I'm not entirely convinced with this addition. CallbackPromiseAdapter exists to
prevent that kind of situation: the Promise has its own lifetime.

This is an alternative. Feel free to ignore:
- you can create MediaSessionCallback<> that has a m_webMediaSession as
Persistent<>
- then, you make m_webMediaSession a Member<> of MediaSession

Then, the WebMediaSession instance would be destroyed when all callbacks and the
MediaSession objects are destroyed.

WDYT?

[davve, 2015/12/08 10:21:23]

I think it's an interesting idea and it matches better what should happen. It's
the promise that should stay alive, not the media session itself. I'll rebase on
top of your metadata patch, with ActiveDOMObject reverted, and investigate
further.

[philipj_slow, 2015/12/08 10:38:45]

Something like this should work, but the lifetime of WebMediaSessio would have
to be independent of the MediaSession. The callbacks would have to have a keep
the WebMediaSession alive and vice-versa.

[davve, 2015/12/09 11:20:18]

I punted on this issue in ps#11 by not involving the session at all when
resolving the promise. I guess we have to revisit when adding event or such so
that the promise needs to keep the blink session alive.

+
     DEFINE_INLINE_TRACE() { }
 
 private:
     friend class MediaSessionTest;
 
-    explicit MediaSession(PassOwnPtr<WebMediaSession>);
+    MediaSession(ExecutionContext*, PassOwnPtr<WebMediaSession>);
 
     OwnPtr<WebMediaSession> m_webMediaSession;
 };