Refactor MediaSourceDelegate destruction.

content/renderer/media/android/webmediaplayer_android.cc

Index: content/renderer/media/android/webmediaplayer_android.cc
diff --git a/content/renderer/media/android/webmediaplayer_android.cc b/content/renderer/media/android/webmediaplayer_android.cc
index 27e2c1d8e698bd11d66049ff033363b72e5f3011..8de6f4ebb88cecfd5f0c99c4649d85ea8826b146 100644
--- a/content/renderer/media/android/webmediaplayer_android.cc
+++ b/content/renderer/media/android/webmediaplayer_android.cc
@@ -201,6 +201,16 @@ WebMediaPlayerAndroid::~WebMediaPlayerAndroid() {
     delegate_->PlayerGone(this);
 
   stream_texture_factory_->RemoveObserver(this);
+
+  if (media_source_delegate_) {
+    // Part of |media_source_delegate_| needs to be stopped on the media thread.
+    // Wait until |media_source_delegate_| is fully stopped before tearing
+    // down other objects.
+    base::WaitableEvent waiter(false, false);
+    media_source_delegate_->Stop(
+        base::Bind(&base::WaitableEvent::Signal, base::Unretained(&waiter)));

[qinmin, 2014/09/26 18:06:50]

How about moving this waitableEvent into MediaSourceDelegate::Stop()? 
With the current change, MediaSourceDelegate::Stop() implicitly implies that
only a waitableEvent::signal callback can be accept as the callback will be
executed on another thread. So developers can easily make a mistake there if
they don't read the implementation.

By moving the waitableEvent into MediaSourceDelegate::Stop(), we don't need to
pass a CB into MSD and there is no need to worry about what kind of callbacks
can be passed. 

[xhwang, 2014/09/26 21:06:57]

My Clank checkout is broken.. I'll land this CL as is and address this comment
later.

+    waiter.Wait();
+  }
 }
 
 void WebMediaPlayerAndroid::load(LoadType load_type,