GPU: Fix NULL gpu::Buffer dereference.

gpu/command_buffer/service/command_buffer_service.cc

 // Copyright (c) 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 "gpu/command_buffer/service/command_buffer_service.h"
 
 #include <limits>
 
 #include "base/logging.h"
 #include "base/debug/trace_event.h"
@@ skipping 70 matching lines @@
 
   put_offset_ = put_offset;
 
   if (!put_offset_change_callback_.is_null())
     put_offset_change_callback_.Run();
 }
 
 void CommandBufferService::SetGetBuffer(int32 transfer_buffer_id) {
   DCHECK_EQ(-1, ring_buffer_id_);
   DCHECK_EQ(put_offset_, get_offset_);  // Only if it's empty.
+  // If the buffer is invalid we handle it gracefully.
+  // This means ring_buffer_ can be NULL.
   ring_buffer_ = GetTransferBuffer(transfer_buffer_id);
-  DCHECK(ring_buffer_);
   ring_buffer_id_ = transfer_buffer_id;
-  num_entries_ = ring_buffer_->size() / sizeof(CommandBufferEntry);
+  int32 size = ring_buffer_ ? ring_buffer_->size() : 0;
+  num_entries_ = size / sizeof(CommandBufferEntry);
   put_offset_ = 0;
   SetGetOffset(0);
   if (!get_buffer_change_callback_.is_null()) {
     get_buffer_change_callback_.Run(ring_buffer_id_);
   }
 
   UpdateState();
 }
 
 bool CommandBufferService::SetSharedStateBuffer(
@@ skipping 83 matching lines @@
     const GetBufferChangedCallback& callback) {
   get_buffer_change_callback_ = callback;
 }
 
 void CommandBufferService::SetParseErrorCallback(
     const base::Closure& callback) {
   parse_error_callback_ = callback;
 }
 
 }  // namespace gpu