Don't attempt to forward declare StringPiece.

chrome/test/base/v8_unit_test.h

Index: chrome/test/base/v8_unit_test.h
diff --git a/chrome/test/base/v8_unit_test.h b/chrome/test/base/v8_unit_test.h
index 9391dae8a9a5d5a259d9560ce1228316671ba7a4..d61da81b59df74597101abd29af8aadb33c9d747 100644
--- a/chrome/test/base/v8_unit_test.h
+++ b/chrome/test/base/v8_unit_test.h
@@ -10,13 +10,10 @@
 #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.