Don't iterate over a 0 mask resource in RenderPassDrawQuad

cc/quads/draw_quad_unittest.cc

 // Copyright 2012 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/draw_quad.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
@@ skipping 752 matching lines @@
                       mask_resource_id,
                       contents_changed_since_last_frame,
                       mask_u_v_rect,
                       filters,
                       filter,
                       background_filters,
                       copied_render_pass_id);
   EXPECT_EQ(mask_resource_id, quad_new->mask_resource_id);
   EXPECT_EQ(1, IterateAndCount(quad_new.get()));
   EXPECT_EQ(mask_resource_id + 1, quad_new->mask_resource_id);
+  quad_new->mask_resource_id = 0;
+  EXPECT_EQ(0, IterateAndCount(quad_new.get()));
+  EXPECT_EQ(0u, quad_new->mask_resource_id);
 }
 
 TEST_F(DrawQuadIteratorTest, SolidColorDrawQuad) {
   SkColor color = 0x49494949;
 
   CREATE_SHARED_STATE();
   CREATE_QUAD_1_NEW(SolidColorDrawQuad, color);
   EXPECT_EQ(0, IterateAndCount(quad_new.get()));
 }
 
@@ skipping 92 matching lines @@
                     texture_size,
                     swizzle_contents,
                     content_rect,
                     contents_scale,
                     picture_pile);
   EXPECT_EQ(0, IterateAndCount(quad_new.get()));
 }
 
 }  // namespace
 }  // namespace cc