Use scroll customization primitives for touch scrolling (behind REF).

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 4b537da96697fc986e6a635ec6f795282d6f8996..a5b04bc2934970dac721ad3256c5943a3baf29c5 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -113,6 +113,7 @@
 #include "core/page/Page.h"
 #include "core/page/PointerLockController.h"
 #include "core/page/SpatialNavigation.h"
+#include "core/page/scrolling/ScrollState.h"
 #include "core/svg/SVGDocumentExtensions.h"
 #include "core/svg/SVGElement.h"
 #include "platform/EventDispatchForbiddenScope.h"
@@ -481,6 +482,70 @@ void Element::scrollIntoViewIfNeeded(bool centerIfNeeded)
         renderer()->scrollRectToVisible(bounds, ScrollAlignment::alignToEdgeIfNeeded, ScrollAlignment::alignToEdgeIfNeeded);
 }
 
+void Element::distributeScroll(ScrollState* scrollState)
+{
+    ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
+    ASSERT(scrollState);
+    if (!scrollState || scrollState->fullyConsumed())
+        return;
+
+    scrollState->distributeToScrollChainDescendant();
+
+    // If the scroll doesn't propagate, and we're currently scrolling
+    // an element other than this one, don't scroll.
+    if (!scrollState->shouldPropagate()
+        && scrollState->deltaConsumedForScrollSequence()
+        && scrollState->currentNativeScrollingElement() != this) {
+        return;
+    }
+
+    const double deltaX = scrollState->deltaX();
+    const double deltaY = scrollState->deltaY();
+
+    applyScroll(scrollState);
+
+    if (deltaX != scrollState->deltaX() || deltaY != scrollState->deltaY())
+        scrollState->setCurrentNativeScrollingElement(this);
+}
+
+void Element::applyScroll(ScrollState* scrollState)
+{
+    ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
+    ASSERT(scrollState);
+    if (!scrollState || scrollState->fullyConsumed())
+        return;
+
+    const double deltaX = scrollState->deltaX();
+    const double deltaY = scrollState->deltaY();
+    bool scrolled = false;
+
+    // Handle the documentElement separately, as it scrolls the FrameView.
+    if (this == document().documentElement()) {
+        FloatSize delta(deltaX, deltaY);
+        if (document().frame()->applyScrollDelta(delta, scrollState->isBeginning()))
+            scrolled = true;
+    } else {
+        LayoutBox* curBox = renderer()->enclosingBox();
+        if (deltaX && curBox->scroll(ScrollLeft, ScrollByPrecisePixel, deltaX))
+            scrolled = true;
+
+        if (deltaY && curBox->scroll(ScrollUp, ScrollByPrecisePixel, deltaY))
+            scrolled = true;
+    }
+
+    if (!scrolled)
+        return;
+
+    // We need to setCurrentNativeScrollingElement in both the
+    // distributeScroll and applyScroll default implementations so
+    // that if JS overrides one of these methods, but not the
+    // other, this bookkeeping remains accurate.
+    scrollState->setCurrentNativeScrollingElement(this);
+    scrollState->consumeDeltaNative(scrollState->deltaX(), scrollState->deltaY());
+    if (scrollState->fromUserInput())
+        document().frame()->view()->setWasScrolledByUser(true);
+};
+
 static float localZoomForRenderer(LayoutObject& renderer)
 {
     // FIXME: This does the wrong thing if two opposing zooms are in effect and canceled each