Don't attempt to forward declare StringPiece.

chrome/test/base/v8_unit_test.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_TEST_BASE_V8_UNIT_TEST_H_
 #define CHROME_TEST_BASE_V8_UNIT_TEST_H_
 #pragma once
 
 #include <string>
 #include <vector>
 
 #include "base/file_path.h"
+#include "base/string_piece.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "v8/include/v8.h"
 
-namespace base {
-class StringPiece;
-}
-
 // A superclass for unit tests that involve running JavaScript.  This class
 // sets up V8 context and has methods that make it easy to execute scripts in
 // this context as well as call functions in the context.
 class V8UnitTest : public testing::Test {
  public:
   V8UnitTest();
   virtual ~V8UnitTest();
 
   // Methods from testing::Test.
   virtual void SetUp() OVERRIDE;
@@ skipping 52 matching lines @@
   v8::HandleScope handle_scope_;
 
   // Context for the JavaScript in the test.
   v8::Handle<v8::Context> context_;
 
   // User added libraries.
   std::vector<FilePath> user_libraries_;
 };
 
 #endif  // CHROME_TEST_BASE_V8_UNIT_TEST_H_