Monitor the intersection of video and viewport.

media/remoting/remoting_controller.cc

Index: media/remoting/remoting_controller.cc
diff --git a/media/remoting/remoting_controller.cc b/media/remoting/remoting_controller.cc
index 73c372f68673518e429677979a24dbd83fd66864..3511e1cc683ff83e563fbb2602accc6a17590c1f 100644
--- a/media/remoting/remoting_controller.cc
+++ b/media/remoting/remoting_controller.cc
@@ -142,6 +142,37 @@ void RemotingController::OnExitedFullscreen() {
   UpdateAndMaybeSwitch();
 }
 
+void RemotingController::OnVideoViewportRatioChanged(float ratio) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+
+  // Reset on any notification, since this indicates the user is scrolling
+  // around in the document, the document is changing layout, etc.
+  viewport_fill_debouncer_timer_.Stop();
+
+  // Dropping below the threshold should instantly stop remote rendering.
+  if (ratio < 0.85) {
+    if (is_mostly_filling_viewport_) {
+      is_mostly_filling_viewport_ = false;
+      UpdateAndMaybeSwitch();
+    }
+    return;
+  }
+
+  // Meeting/Exceeding the threshold should hold steady for 5 seconds before
+  // starting remote rendering.
+  if (!is_mostly_filling_viewport_) {
+    viewport_fill_debouncer_timer_.Start(
+        FROM_HERE, base::TimeDelta::FromSeconds(5),
+        base::Bind(&RemotingController::OnViewportMostlyFilledAndUnchanging,
+                   weak_factory_.GetWeakPtr()));
+  }
+}
+
+void RemotingController::OnViewportMostlyFilledAndUnchanging() {
+  is_mostly_filling_viewport_ = true;
+  UpdateAndMaybeSwitch();
+}
+
 void RemotingController::OnSetCdm(CdmContext* cdm_context) {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
@@ -232,13 +263,11 @@ bool RemotingController::ShouldBeRemoting() {
 
   if (!is_sink_available_)
     return false;
-  if (!is_fullscreen_)
-    return false;
   if (has_video_ && !IsVideoCodecSupported())
     return false;
   if (has_audio_ && !IsAudioCodecSupported())
     return false;
-  return true;
+  return is_fullscreen_ || is_mostly_filling_viewport_;
 }
 
 void RemotingController::UpdateAndMaybeSwitch() {