Make all gesture scrolls use customization path internally

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

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index ebaa903a39c876845428c9f71fc889bc35ced02e..419782a00a570fcf513f96a2217ce0836403f50b 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -538,8 +538,6 @@ void Element::callDistributeScroll(ScrollState& scrollState)
 
 void Element::nativeApplyScroll(ScrollState& scrollState)
 {
-    DCHECK(RuntimeEnabledFeatures::scrollCustomizationEnabled());
-
     // All elements in the scroll chain should be boxes.
     DCHECK(!layoutObject() || layoutObject()->isBox());
 
@@ -556,8 +554,9 @@ void Element::nativeApplyScroll(ScrollState& scrollState)
 
     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());
@@ -567,7 +566,7 @@ void Element::nativeApplyScroll(ScrollState& scrollState)
 
     ScrollResult result =
         LayoutBoxItem(boxToScroll).enclosingBox().scroll(
-            ScrollByPrecisePixel,
+            ScrollGranularity(static_cast<int>(scrollState.deltaGranularity())),
             delta);
 
     if (!result.didScroll())