Add minimal implementation of unprefixed MediaSource API that has feature parity with prefixed API

Source/modules/mediasource/MediaSourceBase.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 158 matching lines @@
 }
 
 bool MediaSourceBase::hasPendingActivity() const
 {
     return m_private || m_asyncEventQueue->hasPendingEvents()
         || ActiveDOMObject::hasPendingActivity();
 }
 
 void MediaSourceBase::stop()
 {
+    m_asyncEventQueue->close();
+    if (!isClosed())
+        setReadyState(closedKeyword());
     m_private.clear();
-    m_asyncEventQueue->cancelAllEvents();
 }
 
 PassOwnPtr<SourceBufferPrivate> MediaSourceBase::createSourceBufferPrivate(const String& type, const MediaSourcePrivate::CodecsArray& codecs, ExceptionCode& ec)
 {
     OwnPtr<SourceBufferPrivate> sourceBufferPrivate;
     switch (m_private->addSourceBuffer(type, codecs, &sourceBufferPrivate)) {
     case MediaSourcePrivate::Ok: {
         return sourceBufferPrivate.release();
     }
     case MediaSourcePrivate::NotSupported:
@@ skipping 49 matching lines @@
 {
     MemoryClassInfo info(memoryObjectInfo, this, WebCoreMemoryTypes::DOM);
     ActiveDOMObject::reportMemoryUsage(memoryObjectInfo);
     info.addMember(m_eventTargetData, "eventTargetData");
     info.addMember(m_readyState, "readyState");
     info.addMember(m_private, "private");
     info.addMember(m_asyncEventQueue, "asyncEventQueue");
 }
 
 }