Remove unneeded includes of base/string_piece.h

chrome/test/v8_unit_test.h

Index: chrome/test/v8_unit_test.h
===================================================================
--- chrome/test/v8_unit_test.h	(revision 13095)
+++ chrome/test/v8_unit_test.h	(working copy)
@@ -7,10 +7,11 @@
 
 #include <string>
 
-#include "base/string_piece.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "v8/include/v8.h"
 
+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.