DelegatedFrameHost: Prevent FrameSubscriber captures if damage_rect is empty.

content/browser/renderer_host/delegated_frame_host.cc

Index: content/browser/renderer_host/delegated_frame_host.cc
diff --git a/content/browser/renderer_host/delegated_frame_host.cc b/content/browser/renderer_host/delegated_frame_host.cc
index 60c10005ac273960cdfd3f5c268476719f36295c..6ea4299f297d795129ebb476927ee5d32c3698b4 100644
--- a/content/browser/renderer_host/delegated_frame_host.cc
+++ b/content/browser/renderer_host/delegated_frame_host.cc
@@ -544,7 +544,11 @@ void DelegatedFrameHost::ReturnResources(
 
 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);
 }