Rename 'instant' value of scroll-behavior CSS property to 'auto'

Source/core/rendering/style/RenderStyle.h

Index: Source/core/rendering/style/RenderStyle.h
diff --git a/Source/core/rendering/style/RenderStyle.h b/Source/core/rendering/style/RenderStyle.h
index 7b7785a9a4b02bf50fe18c7d5e6711e6481a991f..b1e25aa99489da8f9012c1a131a8c36ab542ecd5 100644
--- a/Source/core/rendering/style/RenderStyle.h
+++ b/Source/core/rendering/style/RenderStyle.h
@@ -1643,7 +1643,7 @@ public:
     static TouchAction initialTouchAction() { return TouchActionAuto; }
     static ShadowList* initialBoxShadow() { return 0; }
     static ShadowList* initialTextShadow() { return 0; }
-    static ScrollBehavior initialScrollBehavior() { return ScrollBehaviorInstant; }
+    static ScrollBehavior initialScrollBehavior() { return ScrollBehaviorAuto; }
     static ScrollBlocksOn initialScrollBlocksOn() { return ScrollBlocksOnNone; }
 
     // The initial value is 'none' for grid tracks.