cc: early return if unoccluded_region_in_target_surface is empty

R=danakj@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/381613004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282980 0039d316-1c4b-4281-b951-d872f2087c98

cc/trees/occlusion_tracker.cc

@@ -567,6 +567,9 @@ gfx::Rect OcclusionTracker<LayerType>::UnoccludedContentRect(
   unoccluded_region_in_target_surface.Subtract(
       stack_.back().occlusion_from_outside_target);
 
+  if (unoccluded_region_in_target_surface.IsEmpty())
+    return gfx::Rect();
+
   gfx::Rect unoccluded_rect_in_target_surface =
       unoccluded_region_in_target_surface.bounds();
   gfx::Rect unoccluded_rect = MathUtil::ProjectEnclosingClippedRect(
@@ -609,6 +612,9 @@ gfx::Rect OcclusionTracker<LayerType>::UnoccludedContributingSurfaceContentRect(
   unoccluded_region_in_target_surface.Subtract(
       second_last.occlusion_from_outside_target);
 
+  if (unoccluded_region_in_target_surface.IsEmpty())
+    return gfx::Rect();
+
   gfx::Rect unoccluded_rect_in_target_surface =
       unoccluded_region_in_target_surface.bounds();
   gfx::Rect unoccluded_rect = MathUtil::ProjectEnclosingClippedRect(