NOT FOR LANDING Implement WebMediaSession

content/renderer/renderer_blink_platform_impl.h

Index: content/renderer/renderer_blink_platform_impl.h
diff --git a/content/renderer/renderer_blink_platform_impl.h b/content/renderer/renderer_blink_platform_impl.h
index 86264e1a67e2a7248a13ab7a930c7761cf928795..f4a70df0631565dac6dfbd08bfb7bf6cf29846d7 100644
--- a/content/renderer/renderer_blink_platform_impl.h
+++ b/content/renderer/renderer_blink_platform_impl.h
@@ -76,6 +76,7 @@ class CONTENT_EXPORT RendererBlinkPlatformImpl : public BlinkPlatformImpl {
   virtual bool isLinkVisited(unsigned long long linkHash);
   virtual void createMessageChannel(blink::WebMessagePortChannel** channel1,
                                     blink::WebMessagePortChannel** channel2);
+  virtual blink::WebMediaSession* createMediaSession();

[whywhat, 2015/07/30 14:31:22]

As I understand, hanging media session from BlinkPlatform means that each
MediaSession (or its creation) won't be tied to any particular frame on the page
so implementing any per-frame logic if needed would be hard. If that's not a
problem, having createMediaSession here seems alright.

Otherwise MediaSession sounds more like PresentationRequest:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...
It can just be constructed with an ExecutionContext where it gets the frame
from.

[philipj_slow, 2015/07/30 14:47:04]

Even though Blink-created MediaSessions won't have the per-tab sharing that the
default sessions have, it will be necessary to associate it with a tab so that
one can click the notification to get back to the responsible tab. I guess that
rules out the BlinkPlatform path. Thanks :)
Looks familiar, I looked at it a bit before. In for example
PresentationRequest::start, is ongoing request in any way tied to the
PresentationRequest instance that started it? It looks like the
WebPresentationClient involved is tied to the frame via the
PresentationController. It might be that MediaSession will need a callback to
the same instance to update some state (idle, active, interrupted) right before
the promise is resolved, so that scripts can't observe the change first.

I see that Presentation uses Mojo for the IPC, is that something you would
recommend in this case too?

[mlamouri (slow - plz ping), 2015/08/05 15:50:16]

As Anton pointed, RenderBlinkPlatformImpl isn't the best way to do that. You
should have the MediaSession available from the WebFrameClient (implemented by
RenderFrameImpl).
I guess we could have a MediaSessionService. Otherwise, you can just add new
Media IPC.

   virtual blink::WebPrescientNetworking* prescientNetworking();
   virtual void cacheMetadata(const blink::WebURL&, int64, const char*, size_t);
   virtual blink::WebString defaultLocale();