Cleanup remaining class/struct fwd declarations

tools/gn/xcode_writer.h

 // Copyright 2016 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_XCODE_WRITER_H_
 #define TOOLS_GN_XCODE_WRITER_H_
 
 #include <iosfwd>
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 
 class Builder;
 class BuildSettings;
 class Err;
 class SourceDir;
 class Target;
 
 using PBXAttributes = std::map<std::string, std::string>;
 class PBXProject;
 
-namespace base {
-class FilePath;
-}
-
 class XcodeWriter {
  public:
   enum TargetOsType {
     WRITER_TARGET_OS_IOS,
     WRITER_TARGET_OS_MACOS,
   };
 
   // Writes Xcode workspace and project files.
   //
   // |workspace_name| is the optional name of the workspace file name ("all"
@@ skipping 55 matching lines @@
   void WriteWorkspaceContent(std::ostream& out);
   void WriteProjectContent(std::ostream& out, PBXProject* project);
 
   std::string name_;
   std::vector<std::unique_ptr<PBXProject>> projects_;
 
   DISALLOW_COPY_AND_ASSIGN(XcodeWriter);
 };
 
 #endif  // TOOLS_GN_XCODE_WRITER_H_