Update from https://crrev.com/306655

gpu/command_buffer/client/cmd_buffer_helper.h

 // 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.
 
 // This file contains the command buffer helper class.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 #define GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 
 #include <string.h>
@@ skipping 119 matching lines @@
     CommandBufferEntry* space = &entries_[put_];
     put_ += entries;
     immediate_entry_count_ -= entries;
 
     DCHECK_LE(put_, total_entry_count_);
     return space;
   }
 
   template <typename T>
   void ForceNullCheck(T* data) {
-#if defined(OS_WIN) && defined(ARCH_CPU_64_BITS)
+#if defined(COMPILER_MSVC) && defined(ARCH_CPU_64_BITS) && !defined(__clang__)
     // 64-bit MSVC's alias analysis was determining that the command buffer
     // entry couldn't be NULL, so it optimized out the NULL check.
     // Dereferencing the same datatype through a volatile pointer seems to
     // prevent that from happening. http://crbug.com/361936
+    // TODO(jbauman): Remove once we're on VC2015, http://crbug.com/412902
     if (data)
       static_cast<volatile T*>(data)->header;
 #endif
   }
 
   // Typed version of GetSpace. Gets enough room for the given type and returns
   // a reference to it.
   template <typename T>
   T* GetCmdSpace() {
     COMPILE_ASSERT(T::kArgFlags == cmd::kFixed, Cmd_kArgFlags_not_kFixed);
@@ skipping 178 matching lines @@
   // Can be used to track when prior commands have been flushed.
   uint32 flush_generation_;
 
   friend class CommandBufferHelperTest;
   DISALLOW_COPY_AND_ASSIGN(CommandBufferHelper);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_