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

Source/core/dom/shadow/ComposedTreeTraversalTest.cpp

 // Copyright 2015 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.
 
 #include "config.h"
 #include "core/dom/shadow/ComposedTreeTraversal.h"
 
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/dom/Node.h"
 #include "core/dom/NodeTraversal.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/frame/FrameView.h"
 #include "core/html/HTMLDocument.h"
 #include "core/html/HTMLElement.h"
 #include "core/testing/DummyPageHolder.h"
 #include "platform/geometry/IntSize.h"
 #include "wtf/Compiler.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/Vector.h"
-#include "wtf/testing/WTFTestHelpers.h"
 #include <gtest/gtest.h>
 
 namespace blink {
 
 class ComposedTreeTraversalTest : public ::testing::Test {
 protected:
     HTMLDocument& document() const;
 
     // Sets |mainHTML| to BODY element with |innerHTML| property and attaches
     // shadow root to child with |shadowHTML|, then update distribution for
@@ skipping 283 matching lines @@
     EXPECT_EQ(*m2, ComposedTreeTraversal::lastWithinOrSelf(*m2));
 
     EXPECT_EQ(s11->firstChild(), ComposedTreeTraversal::lastWithin(*s11));
     EXPECT_EQ(*s11->firstChild(), ComposedTreeTraversal::lastWithinOrSelf(*s11));
 
     EXPECT_EQ(m10->firstChild(), ComposedTreeTraversal::lastWithin(*s12));
     EXPECT_EQ(*m10->firstChild(), ComposedTreeTraversal::lastWithinOrSelf(*s12));
 }
 
 } // namespace blink