Support more configurability in GN toolchains

tools/gn/ninja_group_target_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_GROUP_TARGET_WRITER_H_
 #define TOOLS_GN_NINJA_GROUP_TARGET_WRITER_H_
 
 #include "base/compiler_specific.h"
 #include "tools/gn/ninja_target_writer.h"
 
 // Writes a .ninja file for a group target type.
 class NinjaGroupTargetWriter : public NinjaTargetWriter {
  public:
-  NinjaGroupTargetWriter(const Target* target,
-                         const Toolchain* toolchain,
-                         std::ostream& out);
+  NinjaGroupTargetWriter(const Target* target, std::ostream& out);
   virtual ~NinjaGroupTargetWriter();
 
   virtual void Run() OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NinjaGroupTargetWriter);
 };
 
 #endif  // TOOLS_GN_NINJA_GROUP_TARGET_WRITER_H_