cc : Fix occlusion tracking bug for contributing surface

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 2c8fbb82b5d1e26fe3cbaf0d547f46bacc1bfebe..a0bf98e06e22b025df0d71e598c0deb7dbbe3510 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -958,9 +958,29 @@ bool LayerTreeImpl::UpdateDrawProperties(bool update_lcd_text) {
       if (it.represents_contributing_render_surface()) {
         // Surfaces aren't used by the tile raster code, so they can have
         // occlusion regardless of replicas.
+        const RenderSurfaceImpl* occlusion_surface =
+            occlusion_tracker.OcclusionSurfaceForContributingSurface();
+        gfx::Transform draw_transform;
+        if (occlusion_surface) {
+          // We are calculating transform between two render surfaces. So, we

[enne (OOO), 2016/07/14 19:51:41]

I think Apply and Remove look too similar but do very different things, re:
pre-concat vs post-concat.  I think you should either not make them functions
and do that work inline here or add some additional words to the function names
ApplySublayerScaleAtTarget or some such that make it clear that they are not
inverses of each other.

[jaydasika, 2016/07/14 21:00:46]

I have renamed them to PostConcatSublayerScale and ConcatInverseSublayerScale.
In a follow-up, I will make all callers of PostConcat send the target effect
node id to it directly. So these functions will just grab the sublayer scale
from the effect node they are send and concat/postConcat to the transform. 

+          // need to apply the sublayer scale at target and remove the sublayer
+          // scale at source.
+          property_trees()->transform_tree.ComputeTransform(
+              it->render_surface()->TransformTreeIndex(),
+              occlusion_surface->TransformTreeIndex(), &draw_transform);
+          // We don't have to apply sublayer scale when target is root.
+          if (occlusion_surface->TransformTreeIndex() != 0)
+            draw_property_utils::ApplySublayerScale(
+                occlusion_surface->EffectTreeIndex(),
+                property_trees()->effect_tree, &draw_transform);
+          draw_property_utils::RemoveSublayerScale(
+              it->render_surface()->EffectTreeIndex(),
+              property_trees()->effect_tree, &draw_transform);
+        }
+
         Occlusion occlusion =
             occlusion_tracker.GetCurrentOcclusionForContributingSurface(
-                it->render_surface()->draw_transform());
+                draw_transform);
         it->render_surface()->set_occlusion_in_content_space(occlusion);
         // Masks are used to draw the contributing surface, so should have
         // the same occlusion as the surface (nothing inside the surface