cc: Fix negative integer overflow in RenderPass serialization code.

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 {
@@ skipping 53 matching lines @@
   for (auto it = (*out)->quad_list.begin(); it != (*out)->quad_list.end();
        ++it) {
     if (sqs_iter.index() != shared_quad_state_references[it.index()])
       ++sqs_iter;
     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;
+  return (*out)->shared_quad_state_list.empty() ||
+         sqs_iter.index() == (*out)->shared_quad_state_list.size() - 1;
 }
 
 }  // namespace mojo