Align base::hash_map with C++11.

tools/gn/label_ptr.h

 // Copyright (c) 2013 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.
 
 #ifndef TOOLS_GN_LABEL_PTR_H_
 #define TOOLS_GN_LABEL_PTR_H_
 
 #include <functional>
 
 #include "tools/gn/label.h"
@@ skipping 87 matching lines @@
   return a.label == b.label;
 }
 
 template<typename T> inline bool operator<(const LabelPtrPair<T>& a,
                                            const LabelPtrPair<T>& b) {
   return a.label < b.label;
 }
 
 namespace BASE_HASH_NAMESPACE {
 
-#if defined(COMPILER_GCC)
 template<typename T> struct hash< LabelPtrPair<T> > {
   std::size_t operator()(const LabelPtrPair<T>& v) const {
     BASE_HASH_NAMESPACE::hash<Label> h;
     return h(v.label);
   }
 };
-#elif defined(COMPILER_MSVC)
-template<typename T>
-inline size_t hash_value(const LabelPtrPair<T>& v) {
-  return BASE_HASH_NAMESPACE::hash_value(v.label);
-}
-#endif  // COMPILER...
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // TOOLS_GN_LABEL_PTR_H_