Notify WebMediaPlayer when its ancestor enters/exists fullscreen.

third_party/WebKit/Source/web/FullscreenController.cpp

Index: third_party/WebKit/Source/web/FullscreenController.cpp
diff --git a/third_party/WebKit/Source/web/FullscreenController.cpp b/third_party/WebKit/Source/web/FullscreenController.cpp
index cb8efeffd7bb3e843c17fa3f5debc2591e0afc5f..68029b4b7001860d8ad47a61406781f784d91805 100644
--- a/third_party/WebKit/Source/web/FullscreenController.cpp
+++ b/third_party/WebKit/Source/web/FullscreenController.cpp
@@ -31,6 +31,7 @@
 #include "web/FullscreenController.h"
 
 #include "core/dom/Document.h"
+#include "core/dom/ElementTraversal.h"
 #include "core/dom/Fullscreen.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
@@ -86,6 +87,18 @@ void FullscreenController::didEnterFullscreen() {
     if (videoElement->usesOverlayFullscreenVideo() &&
         m_webViewImpl->layerTreeView())
       m_webViewImpl->layerTreeView()->setHasTransparentBackground(true);
+  } else {
+    for (HTMLVideoElement& videoElement :
+         Traversal<HTMLVideoElement>::descendantsOf(*element)) {

[esprehn, 2016/10/11 21:40:04]

I still don't think we should land this. It requires traversing the entire
subtree of the full screen element, which can be a huge section of the page, for
example it's the entire presentation in Google Slides.

+      if (videoElement.webMediaPlayer() &&
+          videoElement.clientWidth() >=
+              videoElement.document().domWindow()->innerWidth() * 0.9 &&
+          videoElement.clientHeight() >=
+              videoElement.document().domWindow()->innerHeight() * 0.9) {
+        videoElement.webMediaPlayer()->enterFullWindow();
+        break;
+      }
+    }
   }
 }
 
@@ -120,6 +133,15 @@ void FullscreenController::didExitFullscreen() {
           m_needsScrollAndScaleRestore = true;
 
         fullscreen->didExitFullscreen();
+
+        for (HTMLVideoElement& videoElement :
+             Traversal<HTMLVideoElement>::descendantsOf(*element)) {
+          if (videoElement.webMediaPlayer() &&
+              videoElement.webMediaPlayer()->isFullWindow()) {
+            videoElement.webMediaPlayer()->exitFullWindow();

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

Test and comment somewhere on what happens if the video element is removed from
the document. That won't exit fullscreen, but it should change the cast mode
back to plain tab mirroring.

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

The WebMediaPlayer get destroyed and the romoting session stopped if the video
element is removed from the document. One media remoting session is only with
one HTMLMediaElement. Other kind of contents will be always rendered locally.

There might be performance issue here as esprehn@ commented. If the video
element is removed from the document, or if there is no video element called
enterFullWindow(), all video descendants will be looked through.

+            break;
+          }
+        }
       }
     }
   }