Update <video muted=""> handling to match spec

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index f298a23c6f26069154a7448f773f8f77a03ff3f6..1333e0606d3df73e611308d17e38b5a74533d2e8 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -408,6 +408,11 @@ public:
     virtual void didBecomeFullscreenElement() { }
     virtual void willStopBeingFullscreenElement() { }
 
+    // Called by the parser when this element's attributes have all been added.
+    // This is needed for <audio>/<video>, where the muted content attribute
+    // should have an effect only if it is present when the element is created.
+    virtual void finishParsingAttributes() { }
+
     // Called by the parser when this element's close tag is reached,
     // signaling that all child tags have been parsed and added.
     // This is needed for <applet> and <object> elements, which can't lay themselves out