Align base::hash_map with C++11.

tools/gn/label.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_H_
 #define TOOLS_GN_LABEL_H_
 
 #include "base/containers/hash_tables.h"
 #include "build/build_config.h"
 #include "tools/gn/source_dir.h"
@@ skipping 89 matching lines @@
  private:
   SourceDir dir_;
   std::string name_;
 
   SourceDir toolchain_dir_;
   std::string toolchain_name_;
 };
 
 namespace BASE_HASH_NAMESPACE {
 
-#if defined(COMPILER_GCC)
 template<> struct hash<Label> {
   std::size_t operator()(const Label& v) const {
     hash<std::string> stringhash;
     return ((stringhash(v.dir().value()) * 131 +
              stringhash(v.name())) * 131 +
             stringhash(v.toolchain_dir().value())) * 131 +
            stringhash(v.toolchain_name());
   }
 };
-#elif defined(COMPILER_MSVC)
-inline size_t hash_value(const Label& v) {
-  return ((hash_value(v.dir().value()) * 131 +
-           hash_value(v.name())) * 131 +
-          hash_value(v.toolchain_dir().value())) * 131 +
-         hash_value(v.toolchain_name());
-}
-#endif  // COMPILER...
 
 }  // namespace BASE_HASH_NAMESPACE
 
 inline void swap(Label& lhs, Label& rhs) {
   lhs.swap(rhs);
 }
 
 #endif  // TOOLS_GN_LABEL_H_