Fix cc unit tests that depend on verify_property_trees=true

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index 9c1b5b942db7574c3c00d68193a4d0ef0299fbc5..121d3799207afb0233e4e7498c57c367fcb2ceb7 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -132,6 +132,7 @@ class CC_EXPORT LayerTreeImpl {
   void SetPropertyTrees(const PropertyTrees& property_trees) {
     property_trees_ = property_trees;
   }
+  PropertyTrees* property_trees() { return &property_trees_; }
 
   void PushPropertiesTo(LayerTreeImpl* tree_impl);