Use observer pattern instead of sniffing SwapCompositorFrame IPC

content/browser/renderer_host/render_widget_host_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 
 #include <math.h>
 
 #include <set>
 #include <tuple>
@@ skipping 2613 matching lines @@
     return;
   }
   // |has_damage| is not transmitted.
   frame.metadata.begin_frame_ack.has_damage = true;
 
   if (!ui::LatencyInfo::Verify(frame.metadata.latency_info,
                                "RenderWidgetHostImpl::OnSwapCompositorFrame")) {
     std::vector<ui::LatencyInfo>().swap(frame.metadata.latency_info);
   }
 
+  last_frame_metadata_ = frame.metadata.Clone();
+
   latency_tracker_.OnSwapCompositorFrame(&frame.metadata.latency_info);
 
   bool is_mobile_optimized = IsMobileOptimizedFrame(frame.metadata);
   input_router_->NotifySiteIsMobileOptimized(is_mobile_optimized);
   if (touch_emulator_)
     touch_emulator_->SetDoubleTapSupportForPageEnabled(!is_mobile_optimized);
 
   // Ignore this frame if its content has already been unloaded. Source ID
   // is always zero for an OOPIF because we are only concerned with displaying
   // stale graphics on top-level frames. We accept frames that have a source ID
   // greater than |current_content_source_id_| because in some cases the first
   // compositor frame can arrive before the navigation commit message that
   // updates that value.
   if (view_ && frame.metadata.content_source_id >= current_content_source_id_) {
     view_->SubmitCompositorFrame(local_surface_id, std::move(frame));
     view_->DidReceiveRendererFrame();
   } else {
     cc::ReturnedResourceArray resources;
     cc::TransferableResource::ReturnResources(frame.resource_list, &resources);
     SendReclaimCompositorResources(true /* is_swap_ack */, resources);
   }
 
   // After navigation, if a frame belonging to the new page is received, stop
   // the timer that triggers clearing the graphics of the last page.
   if (last_received_content_source_id_ >= current_content_source_id_ &&
       new_content_rendering_timeout_->IsRunning()) {
     new_content_rendering_timeout_->Stop();
   }
+
+  if (delegate_)
+    delegate_->DidReceiveCompositorFrame();
 }
 
 }  // namespace content