Cleanup remaining class/struct fwd declarations

tools/gn/builder.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_BUILDER_H_
 #define TOOLS_GN_BUILDER_H_
 
 #include <map>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "tools/gn/builder_record.h"
 #include "tools/gn/label.h"
 #include "tools/gn/label_ptr.h"
 #include "tools/gn/unique_vector.h"
 
-class Config;
 class Err;
 class Loader;
 class ParseNode;
 
 // The builder assembles the dependency tree. It is not threadsafe and runs on
 // the main thread only. See also BuilderRecord.
 class Builder {
  public:
   typedef base::Callback<void(const BuilderRecord*)> ResolvedGeneratedCallback;
 
@@ skipping 105 matching lines @@
   // Owning pointers.
   typedef std::map<Label, BuilderRecord*> RecordMap;
   RecordMap records_;
 
   ResolvedGeneratedCallback resolved_and_generated_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(Builder);
 };
 
 #endif  // TOOLS_GN_BUILDER_H_