Remove obviously unneeded forward declarations from headers under src/{app,base,net}.

net/base/sdch_filter.h

-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 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.
 
 // SdchFilter applies open_vcdiff content decoding to a datastream.
 // This decoding uses a pre-cached dictionary of text fragments to decode
 // (expand) the stream back to its original contents.
 //
 // This SdchFilter internally uses open_vcdiff/vcdec library to do decoding.
 //
 // SdchFilter is also a subclass of Filter. See the latter's header file
 // filter.h for sample usage.
 
 #ifndef NET_BASE_SDCH_FILTER_H_
 #define NET_BASE_SDCH_FILTER_H_
 #pragma once
 
 #include <string>
 
 #include "base/scoped_ptr.h"
 #include "net/base/filter.h"
 #include "net/base/sdch_manager.h"
 
-class SafeOutputStringInterface;
-
 namespace open_vcdiff {
   class VCDiffStreamingDecoder;
 }
 
 class SdchFilter : public Filter {
  public:
   explicit SdchFilter(const FilterContext& filter_context);
 
   virtual ~SdchFilter();
 
@@ skipping 75 matching lines @@
   GURL url_;
 
   // To facilitate error recovery, allow filter to know if content is text/html
   // by checking within this mime type (we may do a meta-refresh via html).
   std::string mime_type_;
 
   DISALLOW_COPY_AND_ASSIGN(SdchFilter);
 };
 
 #endif  // NET_BASE_SDCH_FILTER_H_