Make canPlayType()'s keySystem argument depend on PrefixedEncryptedMedia

Source/core/html/HTMLMediaElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 691 matching lines @@
     setAttribute(srcAttr, url);
 }
 
 HTMLMediaElement::NetworkState HTMLMediaElement::networkState() const
 {
     return m_networkState;
 }
 
 String HTMLMediaElement::canPlayType(const String& mimeType, const String& keySystem) const
 {
-    if (!keySystem.isNull())
-        UseCounter::countDeprecation(document(), UseCounter::CanPlayTypeKeySystem);
-
     WebMimeRegistry::SupportsType support = supportsType(ContentType(mimeType), keySystem);
     String canPlay;
 
     // 4.8.10.3
     switch (support) {
     case WebMimeRegistry::IsNotSupported:
         canPlay = emptyString();
         break;
     case WebMimeRegistry::MayBeSupported:
         canPlay = "maybe";
@@ skipping 3372 matching lines @@
 
 #if ENABLE(WEB_AUDIO)
 void HTMLMediaElement::clearWeakMembers(Visitor* visitor)
 {
     if (!visitor->isAlive(m_audioSourceNode) && audioSourceProvider())
         audioSourceProvider()->setClient(nullptr);
 }
 #endif
 
 }