Re-introduce printers for Node, Position, PositionAnchorType in GTest

Source/core/dom/Node.h

Index: Source/core/dom/Node.h
diff --git a/Source/core/dom/Node.h b/Source/core/dom/Node.h
index 7a9d06632f33b7ac2fcd757c22fad242af1655c3..dc0b0f822e42ab36d19932514ce099a62915f44f 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -897,6 +897,11 @@ PassRefPtrWillBeRawPtr<T> T::create(Document& document) \
     return adoptRefWillBeNoop(new T(document)); \
 }
 
+// These printers are available only for testing in "webkit_unit_tests", and
+// implemented in "core/testing/CoreTestPrinters.cpp".
+std::ostream& operator<<(std::ostream&, const Node&);
+std::ostream& operator<<(std::ostream&, const Node*);
+
 } // namespace blink
 
 #ifndef NDEBUG