cc: Fix hit-testing in zero-opacity layers.

cc/layers/draw_properties.h

Index: cc/layers/draw_properties.h
diff --git a/cc/layers/draw_properties.h b/cc/layers/draw_properties.h
index 990b4c97d3012ae17464bac28975f90a0220ea27..0508d55571da1b62fd041c31ce1261c7255075e7 100644
--- a/cc/layers/draw_properties.h
+++ b/cc/layers/draw_properties.h
@@ -35,7 +35,8 @@ struct CC_EXPORT DrawProperties {
         index_of_first_descendants_addition(0),
         num_descendants_added(0),
         index_of_first_render_surface_layer_list_addition(0),
-        num_render_surfaces_added(0) {}
+        num_render_surfaces_added(0),
+        layer_or_descendant_has_event_handler(false) {}
 
   // Transforms objects from content space to target surface space, where
   // this layer would be drawn.
@@ -121,6 +122,10 @@ struct CC_EXPORT DrawProperties {
   size_t num_descendants_added;
   size_t index_of_first_render_surface_layer_list_addition;
   size_t num_render_surfaces_added;
+
+  // If true, the layer or some layer in its sub-tree has mousewheel or touch
+  // event handlers,
+  bool layer_or_descendant_has_event_handler;
 };
 
 }  // namespace cc