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

Source/platform/audio/AudioSourceProviderClient.h

Index: Source/platform/audio/AudioSourceProviderClient.h
diff --git a/Source/platform/audio/AudioSourceProviderClient.h b/Source/platform/audio/AudioSourceProviderClient.h
index 1756424c50f97e3172f3e9733a6a4603cadf9d44..c658d9459da521a7159ca4dc4dab4f9439b6a1f5 100644
--- a/Source/platform/audio/AudioSourceProviderClient.h
+++ b/Source/platform/audio/AudioSourceProviderClient.h
@@ -25,13 +25,16 @@
 #ifndef AudioSourceProviderClient_h
 #define AudioSourceProviderClient_h
 
+#include "platform/heap/Handle.h"
+
 namespace WebCore {
 
-class AudioSourceProviderClient {
+class AudioSourceProviderClient : public WillBeGarbageCollectedMixin {
 public:
     virtual void setFormat(size_t numberOfChannels, float sampleRate) = 0;
     virtual void lock() { }
     virtual void unlock() { }
+    virtual void trace(Visitor*) { }
 protected:
     virtual ~AudioSourceProviderClient() { }
 };