gn: Add 'clean' command.

tools/gn/commands.cc

 // 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.
 
 #include "tools/gn/commands.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/item.h"
 #include "tools/gn/label.h"
 #include "tools/gn/label_pattern.h"
 #include "tools/gn/setup.h"
@@ skipping 19 matching lines @@
 const CommandInfoMap& GetCommands() {
   static CommandInfoMap info_map;
   if (info_map.empty()) {
     #define INSERT_COMMAND(cmd) \
         info_map[k##cmd] = CommandInfo(k##cmd##_HelpShort, \
                                        k##cmd##_Help, \
                                        &Run##cmd);
 
     INSERT_COMMAND(Args)
     INSERT_COMMAND(Check)
+    INSERT_COMMAND(Clean)
     INSERT_COMMAND(Desc)
     INSERT_COMMAND(Gen)
     INSERT_COMMAND(Format)
     INSERT_COMMAND(Help)
     INSERT_COMMAND(Ls)
     INSERT_COMMAND(Refs)
 
     #undef INSERT_COMMAND
   }
   return info_map;
@@ skipping 61 matching lines @@
   }
 
   std::vector<LabelPattern> pattern_vector;
   pattern_vector.push_back(pattern);
   FilterTargetsByPatterns(setup->builder()->GetAllResolvedTargets(),
                           pattern_vector, matches);
   return true;
 }
 
 }  // namespace commands