Changes subtreeShouldRenderToSeparateSurface logic to account for explicit clipping

cc/draw_properties.h

Index: cc/draw_properties.h
diff --git a/cc/draw_properties.h b/cc/draw_properties.h
index e5bf8136ed2f498c0acb31725bac4d1b8c452782..858e4ffe61db03b824d523735b74ccd804f90f3b 100644
--- a/cc/draw_properties.h
+++ b/cc/draw_properties.h
@@ -27,6 +27,7 @@ struct CC_EXPORT DrawProperties {
         , contents_scale_x(1)
         , contents_scale_y(1)
         , num_descendants_that_draw_content(0)
+        , descendants_can_clip_selves(false)
     {
     }
 
@@ -87,6 +88,10 @@ struct CC_EXPORT DrawProperties {
 
     // Does not include this layer itself, only its children and descendants.
     int num_descendants_that_draw_content;
+
+    // If true, every descendant in the sub-tree can clip itself without the
+    // need to use hardware sissoring or a new render target.
+    bool descendants_can_clip_selves;
 };
 
 }  // namespace cc