gn: Add 'clean' command.

tools/gn/commands.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_COMMANDS_H_
 #define TOOLS_GN_COMMANDS_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 14 matching lines @@
 extern const char kArgs[];
 extern const char kArgs_HelpShort[];
 extern const char kArgs_Help[];
 int RunArgs(const std::vector<std::string>& args);
 
 extern const char kCheck[];
 extern const char kCheck_HelpShort[];
 extern const char kCheck_Help[];
 int RunCheck(const std::vector<std::string>& args);
 
+extern const char kClean[];
+extern const char kClean_HelpShort[];
+extern const char kClean_Help[];
+int RunClean(const std::vector<std::string>& args);
+
 extern const char kDesc[];
 extern const char kDesc_HelpShort[];
 extern const char kDesc_Help[];
 int RunDesc(const std::vector<std::string>& args);
 
 extern const char kGen[];
 extern const char kGen_HelpShort[];
 extern const char kGen_Help[];
 int RunGen(const std::vector<std::string>& args);
 
@@ skipping 72 matching lines @@
 // Filters the given list of targets by the given pattern list. This is a
 // helper function for setting up a call to CheckPublicHeaders based on a check
 // filter.
 void FilterTargetsByPatterns(const std::vector<const Target*>& input,
                              const std::vector<LabelPattern>& filter,
                              std::vector<const Target*>* output);
 
 }  // namespace commands
 
 #endif  // TOOLS_GN_COMMANDS_H_