GSB uses delta_hints to calculate scrolling chain.

third_party/WebKit/public/platform/WebGestureEvent.h

Index: third_party/WebKit/public/platform/WebGestureEvent.h
diff --git a/third_party/WebKit/public/platform/WebGestureEvent.h b/third_party/WebKit/public/platform/WebGestureEvent.h
index 4cefc3414fbff56fd901ad0531a5c6027fcf9ee3..ead9df77a8780e103f8ebcdf77c71245dd90a0e6 100644
--- a/third_party/WebKit/public/platform/WebGestureEvent.h
+++ b/third_party/WebKit/public/platform/WebGestureEvent.h
@@ -87,6 +87,8 @@ class WebGestureEvent : public WebInputEvent {
       // May be redundant with deltaX/deltaY in the first scrollUpdate.
       float delta_x_hint;
       float delta_y_hint;
+
+      bool ignore_delta_hints;
       // Default initialized to ScrollUnits::PrecisePixels.
       ScrollUnits delta_hint_units;
       // If true, this event will skip hit testing to find a scroll