Determine mask UVs based on texture size

cc/test/fake_mask_layer_impl.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/test/fake_mask_layer_impl.h"
 
 #include "base/memory/ptr_util.h"
 
 namespace cc {
 
@@ skipping 12 matching lines @@
     int id,
     scoped_refptr<RasterSource> raster_source,
     Layer::LayerMaskType mask_type) {
   return base::WrapUnique(
       new FakeMaskLayerImpl(tree_impl, id, raster_source, mask_type));
 }
 
 void FakeMaskLayerImpl::GetContentsResourceId(ResourceId* resource_id,
                                               gfx::Size* resource_size) const {
   *resource_id = 0;
+  *resource_size = resource_size_;
 }
 
 }  // namespace cc