[Video] Add dummy video/audio tracks inactive to select them later.

third_party/WebKit/Source/core/html/HTMLMediaElement.h

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.h b/third_party/WebKit/Source/core/html/HTMLMediaElement.h
index 2c9b6bc98bed2ee440b5bf5df6cb41d6ffe494d2..e506a9f4b1c748648e70770477cd405a879809b1 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.h
@@ -94,6 +94,10 @@ class CORE_EXPORT HTMLMediaElement : public HTMLElement,
   static bool isMediaStreamURL(const String& url);
   static bool isHLSURL(const KURL&);
 
+  // If HTMLMediaElement is using MediaTracks (either placeholder or provided
+  // by the page).
+  static bool mediaTracksEnabledInternally();
+
   DECLARE_VIRTUAL_TRACE();
 
   DECLARE_VIRTUAL_TRACE_WRAPPERS();