Don't iterate over a 0 mask resource in RenderPassDrawQuad

cc/quads/render_pass_draw_quad.cc

 // Copyright 2011 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/quads/render_pass_draw_quad.h"
 
 namespace cc {
 
 RenderPassDrawQuad::RenderPassDrawQuad()
     : render_pass_id(RenderPass::Id(-1, -1)),
@@ skipping 65 matching lines @@
   this->mask_resource_id = mask_resource_id;
   this->contents_changed_since_last_frame = contents_changed_since_last_frame;
   this->mask_uv_rect = mask_uv_rect;
   this->filters = filters;
   this->filter = filter;
   this->background_filters = background_filters;
 }
 
 void RenderPassDrawQuad::IterateResources(
     const ResourceIteratorCallback& callback) {
-  mask_resource_id = callback.Run(mask_resource_id);
+  if (mask_resource_id)
+    mask_resource_id = callback.Run(mask_resource_id);
 }
 
 const RenderPassDrawQuad* RenderPassDrawQuad::MaterialCast(
     const DrawQuad* quad) {
   DCHECK_EQ(quad->material, DrawQuad::RENDER_PASS);
   return static_cast<const RenderPassDrawQuad*>(quad);
 }
 
 }  // namespace cc