Align base::hash_map with C++11.

tools/gn/output_file.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_OUTPUT_FILE_H_
 #define TOOLS_GN_OUTPUT_FILE_H_
 
 #include <string>
 
 #include "base/containers/hash_tables.h"
@@ skipping 29 matching lines @@
   bool operator<(const OutputFile& other) const {
     return value_ < other.value_;
   }
 
  private:
   std::string value_;
 };
 
 namespace BASE_HASH_NAMESPACE {
 
-#if defined(COMPILER_GCC)
 template<> struct hash<OutputFile> {
   std::size_t operator()(const OutputFile& v) const {
     hash<std::string> h;
     return h(v.value());
   }
 };
-#elif defined(COMPILER_MSVC)
-inline size_t hash_value(const OutputFile& v) {
-  return hash_value(v.value());
-}
-#endif  // COMPILER...
 
 }  // namespace BASE_HASH_NAMESPACE
 
 inline void swap(OutputFile& lhs, OutputFile& rhs) {
   lhs.value().swap(rhs.value());
 }
 
 #endif  // TOOLS_GN_OUTPUT_FILE_H_