Oilpan: Use transition types for HTMLMediaElement and make AudioSourceProviderClient a GC mixin.

Source/core/html/HTMLMediaElement.h

Index: Source/core/html/HTMLMediaElement.h
diff --git a/Source/core/html/HTMLMediaElement.h b/Source/core/html/HTMLMediaElement.h
index 7160b0def0089719ac75e40823c95de1dcd7c0b6..e75051ec6b2446a68b00e196bd1116f2927beb56 100644
--- a/Source/core/html/HTMLMediaElement.h
+++ b/Source/core/html/HTMLMediaElement.h
@@ -514,7 +514,7 @@ private:
 
 #if ENABLE(WEB_AUDIO)
     // This is a weak reference, since m_audioSourceNode holds a reference to us.
-    AudioSourceProviderClient* m_audioSourceNode;
+    RawPtrWillBeMember<AudioSourceProviderClient> m_audioSourceNode;

[haraken, 2014/05/21 16:35:58]

Shouldn't this be a weak member?

[zerny-chromium, 2014/05/22 05:54:32]

It appears to be raw simply to break what would otherwise be a ref cycle. I
can't see any apparent reason that the audioSourceNode must be reclaimed if only
the HTMLMediaElement is referencing it.

[haraken, 2014/05/22 07:33:36]

In the current implementation, it looks like that HTMLMediaElement can outlive
AudioSourceProviderClient. To keep the behavior, I guess this pointer needs to
be weak. (Also the comment in line 516 implies that this point is weak.)

[Mads Ager (chromium), 2014/05/22 08:02:56]

I think what that comment is saying is that this is a raw pointer because
m_audioSourceNode has a RefPtr to us and therefore it would introduce a cycle to
use a RefPtr here. The use of the work "weak" here just means that it is a "raw"
pointer.

I agree with Ian that these objects should just live and die together. As far as
I can tell this pointer is raw just to break a reference cycle between the
HTMLMediaElement and the AudioSourceNode that is providing audio for this
element.

 #endif
 
     friend class MediaController;