gn: Make generation of main build.ninja file deterministic.

tools/gn/ninja_build_writer.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_NINJA_BUILD_WRITER_H_
 #define TOOLS_GN_NINJA_BUILD_WRITER_H_
 
 #include <iosfwd>
 #include <map>
 #include <vector>
 
 #include "base/macros.h"
 #include "tools/gn/path_output.h"
 
 class Builder;
 class BuildSettings;
 class Err;
 class Pool;
 class Settings;
 class Target;
 class Toolchain;
 
 // Generates the toplevel "build.ninja" file. This references the individual
 // toolchain files and lists all input .gn files as dependencies of the
 // build itself.
 class NinjaBuildWriter {
  public:
-  NinjaBuildWriter(
-      const BuildSettings* settings,
-      const std::map<const Settings*, const Toolchain*>& used_toolchains,
-      const Toolchain* default_toolchain,
-      const std::vector<const Target*>& default_toolchain_targets,
-      std::ostream& out,
-      std::ostream& dep_out);
+  NinjaBuildWriter(const BuildSettings* settings,
+                   const std::unordered_map<const Settings*, const Toolchain*>&
+                       used_toolchains,
+                   const Toolchain* default_toolchain,
+                   const std::vector<const Target*>& default_toolchain_targets,
+                   std::ostream& out,
+                   std::ostream& dep_out);
   ~NinjaBuildWriter();
 
   // The design of this class is that this static factory function takes the
   // Builder, extracts the relevant information, and passes it to the class
   // constructor. The class itself doesn't depend on the Builder at all which
   // makes testing much easier (tests integrating various functions along with
   // the Builder get very complicated).
   static bool RunAndWriteFile(
       const BuildSettings* settings,
       const Builder& builder,
       Err* err);
 
   bool Run(Err* err);
 
  private:
   void WriteNinjaRules();
   void WriteAllPools();
   void WriteSubninjas();
   bool WritePhonyAndAllRules(
       Err* err);
 
   void WritePhonyRule(const Target* target, const std::string& phony_name);
 
   const BuildSettings* build_settings_;
 
-  const std::map<const Settings*, const Toolchain*>& used_toolchains_;
+  const std::unordered_map<const Settings*, const Toolchain*>& used_toolchains_;
   const Toolchain* default_toolchain_;
   const std::vector<const Target*>& default_toolchain_targets_;
 
   std::ostream& out_;
   std::ostream& dep_out_;
   PathOutput path_output_;
 
   DISALLOW_COPY_AND_ASSIGN(NinjaBuildWriter);
 };
 
 #endif  // TOOLS_GN_NINJA_BUILD_WRITER_H_