Detect change on the intersection of video and viewport.

media/remoting/remoting_renderer_controller.cc

Index: media/remoting/remoting_renderer_controller.cc
diff --git a/media/remoting/remoting_renderer_controller.cc b/media/remoting/remoting_renderer_controller.cc
index c9cb743cc1e27004115b9bddcdbd55fee64f70e7..d554053ec004a1aa0567035c48d4afe3776e6075 100644
--- a/media/remoting/remoting_renderer_controller.cc
+++ b/media/remoting/remoting_renderer_controller.cc
@@ -60,6 +60,13 @@ void RemotingRendererController::OnExitedFullscreen() {
   UpdateAndMaybeSwitch();
 }
 
+void RemotingRendererController::OnStablyFilledMostViewportChanged(
+    bool is_mostly_filling_viewport) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  is_mostly_filling_viewport_ = is_mostly_filling_viewport;
+  UpdateAndMaybeSwitch();
+}
+
 void RemotingRendererController::OnSetCdm(CdmContext* cdm_context) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
@@ -195,10 +202,10 @@ bool RemotingRendererController::ShouldBeRemoting() {
       (has_audio() && !IsAudioCodecSupported()))
     return false;
 
-  // Normally, entering fullscreen is the signal that starts remote rendering.
-  // However, current technical limitations require encrypted content be remoted
-  // without waiting for a user signal.
-  return is_fullscreen_;
+  // Normally, entering fullscreen or filling most of the viewport is the signal
+  // that starts remote rendering. However, current technical limitations
+  // require encrypted content be remoted without waiting for a user signal.
+  return is_fullscreen_ || is_mostly_filling_viewport_;
 }
 
 void RemotingRendererController::UpdateAndMaybeSwitch() {