Adjust DOMWindow properties to emulate old style pinch semantics

Source/core/frame/LocalDOMWindow.h

Index: Source/core/frame/LocalDOMWindow.h
diff --git a/Source/core/frame/LocalDOMWindow.h b/Source/core/frame/LocalDOMWindow.h
index 99b545ced8dc4c35edb909bfe46c6fd732ed801a..7c54295aed58f99fca4c6686f92039b03452e5c6 100644
--- a/Source/core/frame/LocalDOMWindow.h
+++ b/Source/core/frame/LocalDOMWindow.h
@@ -137,10 +137,14 @@ public:
     bool confirm(const String& message) override;
     String prompt(const String& message, const String& defaultValue) override;
     bool find(const String&, bool caseSensitive, bool backwards, bool wrap, bool wholeWord, bool searchInFrames, bool showDialog) const override;
+
+    // FIXME: ScrollBehaviorSmooth is currently unsupported in PinchViewport.
+    // crbug.com/434497
     void scrollBy(double x, double y, ScrollBehavior = ScrollBehaviorAuto) const override;
     void scrollBy(double x, double y, const ScrollOptions&, ExceptionState&) const override;
     void scrollTo(double x, double y, ScrollBehavior = ScrollBehaviorAuto) const override;
     void scrollTo(double x, double y, const ScrollOptions&, ExceptionState&) const override;
+
     void moveBy(float x, float y) const override;
     void moveTo(float x, float y) const override;
     void resizeBy(float x, float y) const override;