Include HTMLMediaElement.h only where needed

Source/core/html/HTMLMediaSource.h

 /*
  * 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 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef HTMLMediaSource_h
 #define HTMLMediaSource_h
 
-#include "core/html/HTMLMediaElement.h"
 #include "core/html/URLRegistry.h"
 #include "wtf/Forward.h"
 
 namespace blink {
 class WebMediaSource;
 }
 
 namespace WebCore {
 
+class HTMLMediaElement;
 class TimeRanges;
 
 class HTMLMediaSource : public URLRegistrable {
 public:
     static void setRegistry(URLRegistry*);
     static HTMLMediaSource* lookup(const String& url) { return s_registry ? static_cast<HTMLMediaSource*>(s_registry->lookup(url)) : 0; }
 
     void ref() { refHTMLMediaSource(); }
     void deref() { derefHTMLMediaSource(); }
 
@@ skipping 16 matching lines @@
     // URLRegistrable
     virtual URLRegistry& registry() const OVERRIDE { return *s_registry; }
 
 private:
     static URLRegistry* s_registry;
 };
 
 }
 
 #endif