Don't iterate over a 0 mask resource in RenderPassDrawQuad

A 0 mask resource means we don't use a mask, it's a valid value. Don't iterate
over it, because we never want to send 0 to the parent, nor do we want to look
up 0 in the child->parent map.

BUG=None

Review URL: https://codereview.chromium.org/14167007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194689 0039d316-1c4b-4281-b951-d872f2087c98

cc/quads/draw_quad_unittest.cc

@@ -770,6 +770,9 @@ TEST_F(DrawQuadIteratorTest, RenderPassDrawQuad) {
   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) {

cc/quads/render_pass_draw_quad.cc

@@ -83,7 +83,8 @@ void RenderPassDrawQuad::SetAll(
 
 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(