DelegatedFrameHost: Prevent FrameSubscriber captures if damage_rect is empty.

content/browser/renderer_host/delegated_frame_host.cc

 // Copyright 2014 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/delegated_frame_host.h"
 
 #include <algorithm>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 526 matching lines @@
   if (resources.empty())
     return;
   std::copy(resources.begin(), resources.end(),
             std::back_inserter(surface_returned_resources_));
   if (!pending_delegated_ack_count_)
     SendReturnedDelegatedResources(last_output_surface_id_);
 }
 
 void DelegatedFrameHost::WillDrawSurface(cc::SurfaceId id,
                                          const gfx::Rect& damage_rect) {
-  if (id != surface_id_)
+  // Frame subscribers are only interested in changes to the target surface, so
+  // do not attempt capture if |damage_rect| is empty.  This prevents the draws
+  // of parent surfaces from triggering extra frame captures, which can affect
+  // smoothness.
+  if (id != surface_id_ || damage_rect.IsEmpty())
     return;
   AttemptFrameSubscriberCapture(damage_rect);
 }
 
 void DelegatedFrameHost::SetBeginFrameSource(
     cc::BeginFrameSource* begin_frame_source) {
   client_->SetBeginFrameSource(begin_frame_source);
 }
 
 void DelegatedFrameHost::EvictDelegatedFrame() {
@@ skipping 323 matching lines @@
     cc::SurfaceManager* manager = factory->GetSurfaceManager();
     new_layer->SetShowSurface(
         surface_id_, base::Bind(&SatisfyCallback, base::Unretained(manager)),
         base::Bind(&RequireCallback, base::Unretained(manager)),
         current_surface_size_, current_scale_factor_,
         current_frame_size_in_dip_);
   }
 }
 
 }  // namespace content