Introduce printers for Node and Position for ease of developing GTest test files

Source/core/testing/CoreTestHelpers.h

+// 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.
+
+#ifndef CoreTestHelpers_h
+#define CoreTestHelpers_h
+
+#include "core/dom/Position.h"
+#include "wtf/testing/WTFTestHelpers.h"
+
+namespace blink {
+
+class Node;
+
+std::ostream& operator<<(std::ostream&, const Node&);
+std::ostream& operator<<(std::ostream&, const Node*);
+std::ostream& operator<<(std::ostream&, Position::AnchorType);
+std::ostream& operator<<(std::ostream&, const Position&);
+
+} // namespace blink
+
+#endif // CoreTestHelpers_h