Don't attempt to forward declare StringPiece.

chrome/renderer/static_v8_external_string_resource.h

 // Copyright (c) 2011 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 CHROME_RENDERER_EXTENSIONS_STATIC_V8_EXTERNAL_STRING_RESOURCE_H_
 #define CHROME_RENDERER_EXTENSIONS_STATIC_V8_EXTERNAL_STRING_RESOURCE_H_
 #pragma once
 
 #include "base/compiler_specific.h"
 #include "base/string_piece.h"
 #include "v8/include/v8.h"
 
-namespace base {
-class StringPiece;
-}
-
 // A very simple implementation of v8::ExternalAsciiStringResource that just
 // wraps a buffer. The buffer must outlive the v8 runtime instance this resource
 // is used in.
 class StaticV8ExternalAsciiStringResource
     : public v8::String::ExternalAsciiStringResource {
  public:
   explicit StaticV8ExternalAsciiStringResource(const base::StringPiece& buffer);
 
   virtual const char* data() const OVERRIDE;
   virtual size_t length() const OVERRIDE;
 
  private:
   base::StringPiece buffer_;
 };
 
 #endif // CHROME_RENDERER_EXTENSIONS_STATIC_V8_EXTERNAL_STRING_RESOURCE_H_