Fix MSE GC, make it less aggressive, more spec-compliant (Blink CL)

Source/modules/mediasource/MediaSource.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 138 matching lines @@
         // 2. If type contains a MIME type that is not supported ..., then throw a NotSupportedError exception and abort these steps.
         // 3. If the user agent can't handle any more SourceBuffer objects then throw a QuotaExceededError exception and abort these steps
         return 0;
     }
 
     SourceBuffer* buffer = SourceBuffer::create(webSourceBuffer.release(), this, m_asyncEventQueue.get());
     // 6. Add the new object to sourceBuffers and fire a addsourcebuffer on that object.
     m_sourceBuffers->add(buffer);
 
     // 7. Return the new object to the caller.
+    WTF_LOG(Media, "MediaSource::addSourceBuffer(%s) %p -> %p", type.ascii().data(), this, buffer);
     return buffer;
 }
 
 void MediaSource::removeSourceBuffer(SourceBuffer* buffer, ExceptionState& exceptionState)
 {
     WTF_LOG(Media, "MediaSource::removeSourceBuffer() %p", this);
 
     // 2.2 https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html#widl-MediaSource-removeSourceBuffer-void-SourceBuffer-sourceBuffer
 
     // 1. If sourceBuffer specifies an object that is not in sourceBuffers then
@@ skipping 339 matching lines @@
 
     size_t insertPosition = 0;
     while (insertPosition < m_activeSourceBuffers->length()
         && m_sourceBuffers->find(m_activeSourceBuffers->item(insertPosition)) < indexInSourceBuffers) {
         ++insertPosition;
     }
 
     m_activeSourceBuffers->insert(insertPosition, sourceBuffer);
 }
 
+HTMLMediaElement* MediaSource::mediaElement() const
+{
+    return m_attachedElement.get();
+}
+
 bool MediaSource::isClosed() const
 {
     return readyState() == closedKeyword();
 }
 
 void MediaSource::close()
 {
     setReadyState(closedKeyword());
 }
 
@@ skipping 70 matching lines @@
 
     m_asyncEventQueue->enqueueEvent(event.release());
 }
 
 URLRegistry& MediaSource::registry() const
 {
     return MediaSourceRegistry::registry();
 }
 
 } // namespace blink