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

cc/ipc/render_pass_struct_traits.cc

 // Copyright 2016 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/ipc/render_pass_struct_traits.h"
 
 #include "base/numerics/safe_conversions.h"
 #include "cc/ipc/shared_quad_state_struct_traits.h"
 
 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);
   std::unique_ptr<mojo::Array<uint32_t>> sqs_references(
       new mojo::Array<uint32_t>(input->quad_list.size()));
   cc::SharedQuadStateList::ConstIterator sqs_iter =
       input->shared_quad_state_list.begin();
   for (auto it = input->quad_list.begin(); it != input->quad_list.end(); ++it) {
     if ((*it)->shared_quad_state != *sqs_iter)
       ++sqs_iter;
     (*sqs_references)[it.index()] =
         base::checked_cast<uint32_t>(sqs_iter.index());
     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());
+  DCHECK(input->shared_quad_state_list.empty() ||
+         input->shared_quad_state_list.size() - 1 == sqs_iter.index());
   return sqs_references.release();
 }
 
 // static
 void StructTraits<cc::mojom::RenderPass, std::unique_ptr<cc::RenderPass>>::
     TearDownContext(const std::unique_ptr<cc::RenderPass>& input,
                     void* context) {
   // static_cast to ensure the destructor is called.
   delete static_cast<mojo::Array<uint32_t>*>(context);
 }
@@ skipping 29 matching lines @@
     if (shared_quad_state_references[it.index()] != sqs_iter.index())
       return false;
     (*it)->shared_quad_state = *sqs_iter;
     if (!(*it)->shared_quad_state)
       return false;
   }
   return sqs_iter.index() == (*out)->shared_quad_state_list.size() - 1;
 }
 
 }  // namespace mojo