Reset the state of the previous frame if overlay processing is skipped.

cc/output/overlay_processor.cc

Index: cc/output/overlay_processor.cc
diff --git a/cc/output/overlay_processor.cc b/cc/output/overlay_processor.cc
index 73e0a59a9b88dca34157e8f3e96ed3b99baca49d..f1a40c79704f5bb622fe37b482e8f9673266d5bb 100644
--- a/cc/output/overlay_processor.cc
+++ b/cc/output/overlay_processor.cc
@@ -143,12 +143,14 @@ void OverlayProcessor::ProcessForOverlays(
   if (ProcessForCALayers(resource_provider, render_pass, render_pass_filters,
                          render_pass_background_filters, candidates,
                          ca_layer_overlays, damage_rect)) {
+    previous_frame_underlay_rect_ = gfx::Rect();

[liberato (no reviews please), 2017/04/26 18:40:31]

clearing it seems to be the default (and safe) action.  to avoid having this
happen the next time somebody adds an early-out, maybe do this instead near the
top of this fn:

gfx::Rect previous_frame_underlay_rect = previous_frame_underlay_rect_;
previous_frame_underlay_rect_ = gfx::Rect();

then, pass the copy as an argument to UpdateDamageRect, rather than having it
look at the original.  it can update |previous...rect_| if it wants to.

at least, i think that @198 is the only place where we update this to a
non-empty value.

[watk, 2017/04/26 19:20:04]

+1

[AndyWu, 2017/04/26 20:40:53]

Done, thanks for your suggestion.

     return;
   }
 
   if (ProcessForDCLayers(resource_provider, render_pass, render_pass_filters,
                          render_pass_background_filters, candidates,
                          dc_layer_overlays, damage_rect)) {
+    previous_frame_underlay_rect_ = gfx::Rect();
     return;
   }
 
@@ -161,6 +163,8 @@ void OverlayProcessor::ProcessForOverlays(
     UpdateDamageRect(candidates, damage_rect);
     return;
   }
+
+  previous_frame_underlay_rect_ = gfx::Rect();
 }
 
 // Subtract on-top overlays from the damage rect, unless the overlays use