Fix --use-mus-in-renderer for mus+ash

cc/ipc/render_pass_struct_traits.cc

Index: cc/ipc/render_pass_struct_traits.cc
diff --git a/cc/ipc/render_pass_struct_traits.cc b/cc/ipc/render_pass_struct_traits.cc
index 274cbc7004d0d77513d27a2b76ca6151e5f7e538..c893d21af7b97e18a68faab92d8bb9ace2d39fca 100644
--- a/cc/ipc/render_pass_struct_traits.cc
+++ b/cc/ipc/render_pass_struct_traits.cc
@@ -12,7 +12,6 @@ namespace mojo {
 // static
 void* StructTraits<cc::mojom::RenderPass, std::unique_ptr<cc::RenderPass>>::
     SetUpContext(const std::unique_ptr<cc::RenderPass>& input) {
-  DCHECK_GT(input->quad_list.size(), 0u);

[Fady Samuel, 2016/07/13 14:48:47]

A question for piman@: Are empty quad lists considered valid? If so, then these
DCHECKs can be removed. Otherwise something is wrong.

[Peng, 2016/07/13 15:01:13]

Sure. I will ask piman@ review this CL too.

   std::unique_ptr<mojo::Array<uint32_t>> sqs_references(
       new mojo::Array<uint32_t>(input->quad_list.size()));
   cc::SharedQuadStateList::ConstIterator sqs_iter =
@@ -25,7 +24,6 @@ void* StructTraits<cc::mojom::RenderPass, std::unique_ptr<cc::RenderPass>>::
     DCHECK_NE(nullptr, (*it)->shared_quad_state);
     DCHECK_EQ(*sqs_iter, (*it)->shared_quad_state);
   }
-  DCHECK_EQ(input->shared_quad_state_list.size() - 1, sqs_iter.index());

[Fady Samuel, 2016/07/13 14:48:47]

I'd like to preserve this DCHECK if shared_quad_state_list.size() > 0

Maybe DCHECK(shared_quad_state_list.size() == 0 ||
(input->shared_quad_state_list.size() - 1, sqs_iter.index()));

[Peng, 2016/07/13 15:01:13]

Done.

   return sqs_references.release();
 }