Tentatively turn on WebMediaPlayerMS by default.

content/renderer/render_view_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/render_view_impl.h"
 
 #include <algorithm>
 #include <cmath>
 #include <string>
 #include <vector>
@@ skipping 2631 matching lines @@
   }
 
   WebMediaPlayer* media_player =
       content::GetContentClient()->renderer()->OverrideCreateWebMediaPlayer(
           this, frame, client, AsWeakPtr(), collection, audio_source_provider,
           audio_source_provider, message_loop_factory, media_stream_impl_,
           render_media_log);
   if (!media_player) {
     // TODO(wjia): when all patches related to WebMediaPlayerMS have been
     // landed, remove the switch. Refer to crbug.com/142988.
-    if (cmd_line->HasSwitch(switches::kEnableWebMediaPlayerMS)) {
+    if (!cmd_line->HasSwitch(switches::kDisableWebMediaPlayerMS) &&
+        MediaStreamImpl::CheckMediaStream(url)) {
       EnsureMediaStreamImpl();
-      if (media_stream_impl_ && media_stream_impl_->IsMediaStream(url)) {
-        return new webkit_media::WebMediaPlayerMS(
-            frame, client, AsWeakPtr(), media_stream_impl_, render_media_log);
-      }
+      return new webkit_media::WebMediaPlayerMS(
+          frame, client, AsWeakPtr(), media_stream_impl_, render_media_log);
     }
 
     media_player = new webkit_media::WebMediaPlayerImpl(
         frame, client, AsWeakPtr(), collection, audio_source_provider,
         audio_source_provider, message_loop_factory, media_stream_impl_,
         render_media_log);
   }
   return media_player;
 }
 
@@ skipping 3682 matching lines @@
 
   updating_frame_tree_ = true;
   active_frame_id_map_.clear();
 
   target_process_id_ = process_id;
   target_routing_id_ = route_id;
   CreateFrameTree(webview()->mainFrame(), frames);
 
   updating_frame_tree_ = false;
 }