Fix ODR violation that can break WTF::String pretty printing in tests.

Source/wtf/text/StringBuilderTest.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 15 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "wtf/text/StringBuilder.h"
 
 #include "wtf/Assertions.h"
-#include "wtf/testing/WTFTestHelpers.h"
 #include "wtf/text/CString.h"
 #include "wtf/text/CharacterNames.h"
 #include "wtf/text/WTFString.h"
 #include <gtest/gtest.h>
 
 namespace WTF {
 
 namespace {
 
 void expectBuilderContent(const String& expected, const StringBuilder& builder)
@@ skipping 272 matching lines @@
     StringBuilder reference;
     reference.append(replacementCharacter); // Make it UTF-16.
     reference.append(String::number(someNumber));
     StringBuilder test;
     test.append(replacementCharacter);
     test.appendNumber(someNumber);
     EXPECT_EQ(reference, test);
 }
 
 } // namespace WTF