tools/gn: forward declare some base types in trace.h

tools/gn/trace.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/trace.h"
 
 #include <algorithm>
 #include <map>
 #include <sstream>
 #include <vector>
 
+#include "base/command_line.h"
+#include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/json/string_escape.h"
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/label.h"
 
 namespace {
 
@@ skipping 292 matching lines @@
     }
     out << "}";
   }
 
   out << "]}";
 
   std::string out_str = out.str();
   base::WriteFile(file_name, out_str.data(),
                        static_cast<int>(out_str.size()));
 }