gpu: Add out-of-line copy ctors for complex classes.

gpu/config/dx_diag_node.h

 // Copyright (c) 2010 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.
 //
 // A tree of name value pairs that report contain DirectX diagnostic
 // information.
 
 #ifndef GPU_CONFIG_DX_DIAG_NODE_H_
 #define GPU_CONFIG_DX_DIAG_NODE_H_
 
 #include <map>
 #include <string>
 
 #include "gpu/gpu_export.h"
 
 namespace gpu {
 
 struct GPU_EXPORT DxDiagNode {
   DxDiagNode();
+  DxDiagNode(const DxDiagNode& other);
   ~DxDiagNode();
   std::map<std::string, std::string> values;
   std::map<std::string, DxDiagNode> children;
 };
 
 }  // namespace gpu
 
 #endif  // GPU_CONFIG_DX_DIAG_NODE_H_