gn: Diag on distinct toolchains with the same name.

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>
@@ skipping 31 matching lines @@
   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);
+  bool WriteSubninjas(Err* err);
+  bool WritePhonyAndAllRules(Err* err);
 
   void WritePhonyRule(const Target* target, const std::string& phony_name);
 
   const BuildSettings* build_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_;
   PathOutput path_output_;
 
   DISALLOW_COPY_AND_ASSIGN(NinjaBuildWriter);
 };
 
 #endif  // TOOLS_GN_NINJA_BUILD_WRITER_H_