NOT FOR LANDING Implement WebMediaSession

content/renderer/renderer_blink_platform_impl.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_RENDERER_RENDERER_BLINK_PLATFORM_IMPL_H_
 #define CONTENT_RENDERER_RENDERER_BLINK_PLATFORM_IMPL_H_
 
 #include "base/compiler_specific.h"
 #include "base/id_map.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 58 matching lines @@
   virtual blink::WebCookieJar* cookieJar();
   virtual blink::WebThemeEngine* themeEngine();
   virtual blink::WebSpeechSynthesizer* createSpeechSynthesizer(
       blink::WebSpeechSynthesizerClient* client);
   virtual bool sandboxEnabled();
   virtual unsigned long long visitedLinkHash(
       const char* canonicalURL, size_t length);
   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();
   virtual void suddenTerminationChanged(bool enabled);
   virtual blink::WebStorageNamespace* createLocalStorageNamespace();
   virtual blink::Platform::FileHandle databaseOpenFile(
       const blink::WebString& vfs_file_name, int desired_flags);
   virtual int databaseDeleteFile(const blink::WebString& vfs_file_name,
                                  bool sync_dir);
   virtual long databaseGetFileAttributes(
@@ skipping 171 matching lines @@
   device::VibrationManagerPtr vibration_manager_;
 
   IDMap<PlatformEventObserverBase, IDMapOwnPointer> platform_event_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererBlinkPlatformImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDERER_BLINK_PLATFORM_IMPL_H_