cc: Make LayerTreeHost a protected Layer member.

cc/test/fake_layer_tree_host.h

Index: cc/test/fake_layer_tree_host.h
diff --git a/cc/test/fake_layer_tree_host.h b/cc/test/fake_layer_tree_host.h
index 52f02a38ed8accd80d5e2884953606864404d79e..11355ed19d86436e8d931a6d7e516acaaa7dea7e 100644
--- a/cc/test/fake_layer_tree_host.h
+++ b/cc/test/fake_layer_tree_host.h
@@ -56,6 +56,9 @@ class FakeLayerTreeHost : public LayerTreeHost {
   PropertyTrees* property_trees() const {
     return layer_tree_->property_trees();
   }
+  void BuildPropertyTreesForTesting() {
+    layer_tree_->BuildPropertyTreesForTesting();
+  }
 
   LayerImpl* CommitAndCreateLayerImplTree();
   LayerImpl* CommitAndCreatePendingTree();