Monitor the intersection of video and viewport.

media/remoting/remoting_controller.h

Index: media/remoting/remoting_controller.h
diff --git a/media/remoting/remoting_controller.h b/media/remoting/remoting_controller.h
index f565d66d89a5d6b6e8340f9a8a42af296d8e7936..31756886fad284ef9d300ff639b0bb645e46fda0 100644
--- a/media/remoting/remoting_controller.h
+++ b/media/remoting/remoting_controller.h
@@ -7,6 +7,7 @@
 
 #include "base/callback.h"
 #include "base/memory/weak_ptr.h"
+#include "base/timer/timer.h"
 #include "media/base/media_observer.h"
 #include "media/mojo/interfaces/remoting.mojom.h"
 #include "mojo/public/cpp/bindings/binding.h"
@@ -52,12 +53,10 @@ class RemotingController final : public MediaObserver,
   void OnStopped(mojom::RemotingStopReason reason) override;
 
   // MediaObserver implementations.
-  // This is called when the video element or its ancestor enters full screen.
-  // We currently use this as an indicator for immersive playback. May add other
-  // criteria (e.g. the actual display width/height of the video element) in
-  // future.
   void OnEnteredFullscreen() override;
   void OnExitedFullscreen() override;
+  void OnVideoViewportIntersectionChanged(
+      const ViewportIntersectionInfo& info) override;
   void OnSetCdm(CdmContext* cdm_context) override;
   void OnMetadataChanged(const PipelineMetadata& metadata) override;
 
@@ -90,6 +89,10 @@ class RemotingController final : public MediaObserver,
   // Callback from RpcBroker when sending message to remote sink.
   void OnSendMessageToSink(std::unique_ptr<std::vector<uint8_t>> message);
 
+  // Callback from |viewport_fill_debouncer_timer_| when video keeps covering
+  // most of the viewport for a certain time.
+  void OnViewportMostlyFilledAndUnchanging();
+
   // Handle incomging and outgoing RPC message.
   std::unique_ptr<remoting::RpcBroker> rpc_broker_;
 
@@ -111,6 +114,12 @@ class RemotingController final : public MediaObserver,
   bool has_audio_ = false;
   bool has_video_ = false;
 
+  // Indicates whether video covers most of the viewport.
+  bool is_mostly_filling_viewport_ = false;
+  // Video/Viewport ratio meeting/exceeding the threshold should hold steady for
+  // a certain time before attempting to start remoting.
+  base::OneShotTimer viewport_fill_debouncer_timer_;
+
   // The callback to switch the media renderer.
   SwitchRendererCallback switch_renderer_cb_;