cc: Compute mask draw properties directly

cc/trees/draw_property_utils.cc

Index: cc/trees/draw_property_utils.cc
diff --git a/cc/trees/draw_property_utils.cc b/cc/trees/draw_property_utils.cc
index fef5d28d672cbc6909cf6eedcb8717d861e8d15a..0723013b467d8fa9292b88c78f09009618004b03 100644
--- a/cc/trees/draw_property_utils.cc
+++ b/cc/trees/draw_property_utils.cc
@@ -1090,6 +1090,18 @@ void ComputeLayerDrawProperties(LayerImpl* layer,
       layer, bounds_in_target_space, layer->draw_properties().clip_rect);
 }
 
+void ComputeMaskDrawProperties(LayerImpl* mask_layer,
+                               const PropertyTrees* property_trees) {
+  // Mask draw properties are used only for rastering, so most of the draw
+  // properties computed for other layers are not needed.
+  mask_layer->draw_properties().screen_space_transform =
+      ScreenSpaceTransformInternal(mask_layer,
+                                   property_trees->transform_tree.Node(
+                                       mask_layer->transform_tree_index()));
+  mask_layer->draw_properties().visible_layer_rect =
+      gfx::Rect(mask_layer->bounds());

[ajuma, 2016/06/07 17:59:39]

We were previously using the owning layer's bounds as the visible rect
(regardless of what's actually visible). Using the mask layer's own bounds seems
to make more sense. Masks are rastered as a single tile, so the only thing that
seems to matter for the visible rect is empty vs non-empty.

+}
+
 void ComputeSurfaceDrawProperties(const PropertyTrees* property_trees,
                                   RenderSurfaceImpl* render_surface) {
   const ClipNode* clip_node =