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

Source/core/dom/DocumentMarkerControllerTest.cpp

 /*
  * Copyright (c) 2013, Google 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 23 matching lines @@
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #include "core/dom/Document.h"
 #include "core/dom/Range.h"
 #include "core/dom/RenderedDocumentMarker.h"
 #include "core/dom/Text.h"
 #include "core/editing/EphemeralRange.h"
 #include "core/html/HTMLElement.h"
 #include "core/testing/DummyPageHolder.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
-#include "wtf/testing/WTFTestHelpers.h"
 #include <gtest/gtest.h>
 
 namespace blink {
 
 class DocumentMarkerControllerTest : public ::testing::Test {
 protected:
     void SetUp() override;
 
     Document& document() const { return *m_document; }
     DocumentMarkerController& markerController() const { return m_document->markers(); }
@@ skipping 157 matching lines @@
     EXPECT_NE(invalidRect, renderedRects[0]);
 
     div->setAttribute(HTMLNames::styleAttr, "margin: 200px");
     document().updateLayout();
     Vector<IntRect> newRenderedRects = markerController().renderedRectsForMarkers(DocumentMarker::Spelling);
     EXPECT_EQ(1u, newRenderedRects.size());
     EXPECT_NE(renderedRects[0], newRenderedRects[0]);
 }
 
 } // namespace blink