Cleanup remaining class/struct fwd declarations

tools/gn/deps_iterator.h

 // Copyright 2014 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_DEPS_ITERATOR_H_
 #define TOOLS_GN_DEPS_ITERATOR_H_
 
 #include <stddef.h>
 
 #include "tools/gn/label_ptr.h"
 
-class Target;
-
 // Provides an iterator for iterating over multiple LabelTargetVectors to
 // make it convenient to iterate over all deps of a target.
 //
 // This works by maintaining a simple stack of vectors (since we have a fixed
 // number of deps types). When the stack is empty, we've reached the end. This
 // means that the default-constructed iterator == end() for any sequence.
 class DepsIterator {
  public:
   // Creates an empty iterator.
   DepsIterator();
@@ skipping 41 matching lines @@
 
   const DepsIterator& begin() const { return begin_; }
   const DepsIterator& end() const { return end_; }
 
  private:
   DepsIterator begin_;
   DepsIterator end_;
 };
 
 #endif  // TOOLS_GN_DEPS_ITERATOR_H_