Notify WebMediaPlayer when its ancestor enters/exists fullscreen.

third_party/WebKit/Source/web/FrameLoaderClientImpl.cpp

Index: third_party/WebKit/Source/web/FrameLoaderClientImpl.cpp
diff --git a/third_party/WebKit/Source/web/FrameLoaderClientImpl.cpp b/third_party/WebKit/Source/web/FrameLoaderClientImpl.cpp
index db1de678cac7e8bda77e43567030f9960c02da88..5a035b76475f40acf9b3a30ce9cf5a35532752a3 100644
--- a/third_party/WebKit/Source/web/FrameLoaderClientImpl.cpp
+++ b/third_party/WebKit/Source/web/FrameLoaderClientImpl.cpp
@@ -787,9 +787,26 @@ std::unique_ptr<WebMediaPlayer> FrameLoaderClientImpl::createWebMediaPlayer(
   HTMLMediaElementEncryptedMedia& encryptedMedia =
       HTMLMediaElementEncryptedMedia::from(htmlMediaElement);
   WebString sinkId(HTMLMediaElementAudioOutputDevice::sinkId(htmlMediaElement));
-  return wrapUnique(webFrame->client()->createMediaPlayer(
-      source, client, &encryptedMedia, encryptedMedia.contentDecryptionModule(),
-      sinkId));
+  std::unique_ptr<WebMediaPlayer> mediaPlayer =
+      wrapUnique(webFrame->client()->createMediaPlayer(
+          source, client, &encryptedMedia,
+          encryptedMedia.contentDecryptionModule(), sinkId));
+
+  // Notify WebMediaPlayer: if the current media is active fullscreen element;
+  // or is a descendant of the fullscreen element and covers most of the window.
+  Element* fullscreenElement =
+      Fullscreen::currentFullScreenElementFrom(htmlMediaElement.document());
+  if (fullscreenElement == htmlMediaElement) {
+    mediaPlayer->enteredFullscreen();

[foolip, 2016/10/11 09:37:13]

Does the case where the media element itself is the fullscreen element need to
be handled differently?

[xjz, 2016/10/11 19:27:25]

It's currently handled same for Media Remoting. 

[foolip, 2016/10/12 11:51:42]

Yes, but wouldn't it be covered by any heuristic used for when the fullscreen
element is the parent? Doing that would increase confidence that the heuristic
works, as breaking it would break the common case too.

[xjz, 2016/10/12 17:40:57]

The heuristic used for when the fullscreen element is the parent is to check
whether the video occupies most of the tab window. If the media element itself
is the fullscreen element, it should cover the full screen (or window if
full-screen-in-tab), right? So I don't think we need to check that for this
case, unless we want to confirm that the heuristic works on this case.

+  } else if (fullscreenElement->contains(&htmlMediaElement) &&
+             htmlMediaElement.clientWidth() >=
+                 htmlMediaElement.document().domWindow()->innerWidth() * 0.9 &&

[foolip, 2016/10/11 09:37:13]

This check could pass for two videos where one obscures the other. I fear I may
still not understand precisely what is hoped for, is the user experience that
they are casting the whole tab, and if the video gets big enough, this logic
kicks in and just the video is cast instead?

This definitely has the structure of an intervention, of trying to fix the user
experience for pages that could in principle do the right thing themselves
(right?) but aren't doing so.

[xjz, 2016/10/11 19:27:26]

Yes, it could be. I think this case is not common use case, right? If it
happens, only one video will be successfully casted to TV, the other one is
still rendered locally.

I fear I may
Yes, if during mirroring, user clicks full screen button and video gets big
enough, we'll swith to media remoting. We think this scenario indicates that
user is only interested in the video playing back on remote devices (TV). So
we'll stop local rendering, capturing, re-encoding, and just send the original
video stream to ChromeCast to render and play on TV, which can save resources
and improve mirroring quality. Does that make sense?
I agree that there might be cases that don't work quite well. But we now aim at
common use cases. And the remoting mode is easily to switch back to mirroring
mode by exiting full screen. 

+             htmlMediaElement.clientHeight() >=
+                 htmlMediaElement.document().domWindow()->innerHeight() * 0.9) {
+    mediaPlayer->enterFullWindow();
+  }
+
+  return mediaPlayer;
 }
 
 ObjectContentType FrameLoaderClientImpl::getObjectContentType(