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

Source/modules/mediasource/MediaSource.cpp

Index: Source/modules/mediasource/MediaSource.cpp
diff --git a/Source/modules/mediasource/MediaSource.cpp b/Source/modules/mediasource/MediaSource.cpp
index 1cdd99e100834026fb2a287e906edaa27493040c..f1bcbf92f916fb72e6805dfaabedb4a3fc5d925a 100644
--- a/Source/modules/mediasource/MediaSource.cpp
+++ b/Source/modules/mediasource/MediaSource.cpp
@@ -156,6 +156,7 @@ SourceBuffer* MediaSource::addSourceBuffer(const String& type, ExceptionState& e
     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;
 }
 
@@ -515,6 +516,11 @@ void MediaSource::setSourceBufferActive(SourceBuffer* sourceBuffer)
     m_activeSourceBuffers->insert(insertPosition, sourceBuffer);
 }
 
+HTMLMediaElement* MediaSource::mediaElement() const
+{
+    return m_attachedElement.get();
+}
+
 bool MediaSource::isClosed() const
 {
     return readyState() == closedKeyword();