Enable smooth transition when show/hide media remoting interstitial.

third_party/WebKit/Source/core/html/HTMLVideoElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010 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 486 matching lines @@
   if (!remoting_interstitial_) {
     remoting_interstitial_ = new MediaRemotingInterstitial(*this);
     ShadowRoot& shadow_root = EnsureUserAgentShadowRoot();
     shadow_root.InsertBefore(remoting_interstitial_, shadow_root.FirstChild());
     HTMLMediaElement::AssertShadowRootChildren(shadow_root);
   }
   remoting_interstitial_->Show();
 }
 
 void HTMLVideoElement::MediaRemotingStopped() {
-  if (media_remoting_status_ != MediaRemotingStatus::kDisabled)
-    media_remoting_status_ = MediaRemotingStatus::kNotStarted;
+  // Early return because this was already called when media remoting was
+  // disabled.
+  if (media_remoting_status_ == MediaRemotingStatus::kDisabled)
+    return;
+  DCHECK_EQ(media_remoting_status_, MediaRemotingStatus::kStarted);

[mlamouri (slow - plz ping), 2017/04/19 17:58:46]

nit: swap the two parameters -- Also, I can't remember if MediaRemotingStatus is
an enum class but if that's the case, some compilers might not accept this and
you will have to do DCHECK(foo == bar)

[xjz, 2017/04/19 18:08:10]

Done. Yes, MediaRemotingStatus is an enum class. Changed to DCHECK(foo == bar)
now.

   DCHECK(remoting_interstitial_);
+  media_remoting_status_ = MediaRemotingStatus::kNotStarted;
   remoting_interstitial_->Hide();
 }
 
 void HTMLVideoElement::DisableMediaRemoting() {
   if (GetWebMediaPlayer())
     GetWebMediaPlayer()->RequestRemotePlaybackDisabled(true);
   media_remoting_status_ = MediaRemotingStatus::kDisabled;
   MediaRemotingStopped();
 }
 
 }  // namespace blink