Suppress smooth scroll for trackpad scrolls on Mac.

Source/platform/mac/ScrollAnimatorMac.mm

 /*
  * Copyright (C) 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 707 matching lines @@
 }
 #endif
 
 bool ScrollAnimatorMac::scroll(ScrollbarOrientation orientation, ScrollGranularity granularity, float step, float delta)
 {
     m_haveScrolledSincePageLoad = true;
 
     if (!scrollAnimationEnabledForSystem() || !m_scrollableArea->scrollAnimatorEnabled())
         return ScrollAnimator::scroll(orientation, granularity, step, delta);
 
-    if (granularity == ScrollByPixel)
+    if (granularity == ScrollByPixel || granularity == ScrollByPrecisePixel)
         return ScrollAnimator::scroll(orientation, granularity, step, delta);
 
     float currentPos = orientation == HorizontalScrollbar ? m_currentPosX : m_currentPosY;
     float newPos = std::max<float>(std::min<float>(currentPos + (step * delta), m_scrollableArea->maximumScrollPosition(orientation)), m_scrollableArea->minimumScrollPosition(orientation));
     if (currentPos == newPos)
         return false;
 
     NSPoint newPoint;
     if ([m_scrollAnimationHelper.get() _isAnimating]) {
         NSPoint targetOrigin = [m_scrollAnimationHelper.get() targetOrigin];
@@ skipping 620 matching lines @@
         return;
 
     m_visibleScrollerThumbRect = rectInViewCoordinates;
 }
 
 bool ScrollAnimatorMac::canUseCoordinatedScrollbar() {
     return ScrollbarThemeMacCommon::isOverlayAPIAvailable();
 }
 
 } // namespace blink