Make all gesture scrolls use customization path internally

third_party/WebKit/Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 520 matching lines @@
     if (callback->nativeScrollBehavior() != WebNativeScrollBehavior::PerformAfterNativeScroll)
         callback->handleEvent(&scrollState);
     if (callback->nativeScrollBehavior() != WebNativeScrollBehavior::DisableNativeScroll)
         nativeDistributeScroll(scrollState);
     if (callback->nativeScrollBehavior() == WebNativeScrollBehavior::PerformAfterNativeScroll)
         callback->handleEvent(&scrollState);
 };
 
 void Element::nativeApplyScroll(ScrollState& scrollState)
 {
-    DCHECK(RuntimeEnabledFeatures::scrollCustomizationEnabled());
-
     // All elements in the scroll chain should be boxes.
     DCHECK(!layoutObject() || layoutObject()->isBox());
 
     if (scrollState.fullyConsumed())
         return;
 
     FloatSize delta(scrollState.deltaX(), scrollState.deltaY());
 
     if (delta.isZero())
         return;
 
     // TODO(esprehn): This should use updateStyleAndLayoutIgnorePendingStylesheetsForNode.
     document().updateStyleAndLayoutIgnorePendingStylesheets();
 
     LayoutBox* boxToScroll = nullptr;
 
-    // Handle the scrollingElement separately, as it should scroll the viewport.
-    if (this == document().scrollingElement())
+    // We should only ever scroll the effective root scroller this way when the
+    // page removes the default applyScroll (ViewportScrollCallback).
+    if (document().effectiveRootScroller() == this)

[tdresser, 2016/06/23 14:34:29]

Nit: we don't normally use yoda style conditionals - maybe flip this around?

(https://en.wikipedia.org/wiki/Yoda_conditions)

[bokan, 2016/06/23 16:12:30]

Hah, never heard yoda conditionals before :)

Wouldn't flipping this be yoda style though? Since `this` is effectively the
constant?

[tdresser, 2016/06/23 16:16:51]

Hmmm, I was thinking about it the other way, but I guess this is reasonable.

Nevermind.

At least I got to mention yoda conditionals...

         boxToScroll = document().layoutView();
     else if (layoutObject())
         boxToScroll = toLayoutBox(layoutObject());
 
     if (!boxToScroll)
         return;
 
     ScrollResult result =
         LayoutBoxItem(boxToScroll).enclosingBox().scroll(
-            ScrollByPrecisePixel,
+            ScrollGranularity(static_cast<int>(scrollState.deltaGranularity())),
             delta);
 
     if (!result.didScroll())
         return;
 
     // FIXME: Native scrollers should only consume the scroll they
     // apply. See crbug.com/457765.
     scrollState.consumeDeltaNative(delta.width(), delta.height());
 
     // We need to setCurrentNativeScrollingElement in both the
@@ skipping 3136 matching lines @@
 
 DEFINE_TRACE_WRAPPERS(Element)
 {
     if (hasRareData()) {
         visitor->traceWrappers(elementRareData());
     }
     ContainerNode::traceWrappers(visitor);
 }
 
 } // namespace blink