Expose scroll customization for touch to JS (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 f55ea51759ea5c6abe84509bb8d47b5478aaf987..7b9fa75bac3f0a14d6f2c94ef04c91afb74cccd0 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -113,6 +113,7 @@
 #include "core/page/PointerLockController.h"
 #include "core/page/SpatialNavigation.h"
 #include "core/page/scrolling/ScrollState.h"
+#include "core/page/scrolling/ScrollStateCallback.h"
 #include "core/paint/DeprecatedPaintLayer.h"
 #include "core/svg/SVGDocumentExtensions.h"
 #include "core/svg/SVGElement.h"
@@ -470,7 +471,40 @@ void Element::scrollIntoViewIfNeeded(bool centerIfNeeded)
         layoutObject()->scrollRectToVisible(bounds, ScrollAlignment::alignToEdgeIfNeeded, ScrollAlignment::alignToEdgeIfNeeded);
 }
 
-void Element::distributeScroll(ScrollState& scrollState)
+namespace {
+
+NativeScrollBehavior toNativeScrollBehavior(String nativeScrollBehavior)
+{
+    DEFINE_STATIC_LOCAL(const String, disable, ("disable-native-scroll"));
+    DEFINE_STATIC_LOCAL(const String, before, ("perform-before-native-scroll"));
+    DEFINE_STATIC_LOCAL(const String, after, ("perform-after-native-scroll"));
+
+    if (nativeScrollBehavior == disable)
+        return DisableNativeScroll;
+    if (nativeScrollBehavior == before)
+        return PerformBeforeNativeScroll;
+    if (nativeScrollBehavior == after)
+        return PerformAfterNativeScroll;
+
+    ASSERT_NOT_REACHED();
+    return DisableNativeScroll;
+}
+
+} // namespace
+
+void Element::setDistributeScroll(ScrollStateCallback* scrollStateCallback, String nativeScrollBehavior)
+{
+    scrollStateCallback->setNativeScrollBehavior(toNativeScrollBehavior(nativeScrollBehavior));
+    ensureElementRareData().setDistributeScroll(scrollStateCallback);
+}
+
+void Element::setApplyScroll(ScrollStateCallback* scrollStateCallback, String nativeScrollBehavior)
+{
+    scrollStateCallback->setNativeScrollBehavior(toNativeScrollBehavior(nativeScrollBehavior));
+    ensureElementRareData().setApplyScroll(scrollStateCallback);
+}
+
+void Element::nativeDistributeScroll(ScrollState& scrollState)
 {
     ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
     if (scrollState.fullyConsumed())
@@ -490,15 +524,30 @@ void Element::distributeScroll(ScrollState& scrollState)
     const double deltaX = scrollState.deltaX();
     const double deltaY = scrollState.deltaY();
 
-    applyScroll(scrollState);
+    callApplyScroll(scrollState);
 
     if (deltaX != scrollState.deltaX() || deltaY != scrollState.deltaY())
         scrollState.setCurrentNativeScrollingElement(this);
 }
 
-void Element::applyScroll(ScrollState& scrollState)
+void Element::callDistributeScroll(ScrollState& scrollState)
+{
+    if (!hasRareData() || !elementRareData()->getDistributeScroll()) {
+        nativeDistributeScroll(scrollState);
+    } else {
+        ScrollStateCallback& callback = *elementRareData()->getDistributeScroll();
+        if (callback.nativeScrollBehavior() == PerformAfterNativeScroll)
+            nativeDistributeScroll(scrollState);
+        callback.handleEvent(&scrollState);
+        if (callback.nativeScrollBehavior() == PerformBeforeNativeScroll)
+            nativeDistributeScroll(scrollState);
+    }
+};
+
+void Element::nativeApplyScroll(ScrollState& scrollState)
 {
     ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
+
     if (scrollState.fullyConsumed())
         return;
 
@@ -506,8 +555,11 @@ void Element::applyScroll(ScrollState& scrollState)
     const double deltaY = scrollState.deltaY();
     bool scrolled = false;
 
-    // Handle the documentElement separately, as it scrolls the FrameView.
-    if (this == document().documentElement()) {
+    if (deltaY || deltaX)
+        document().updateLayoutIgnorePendingStylesheets();
+
+    // Handle the scrollingElement separately, as it scrolls the FrameView.
+    if (this == document().scrollingElement()) {
         FloatSize delta(deltaX, deltaY);
         if (document().frame()->applyScrollDelta(delta, scrollState.isBeginning()).didScroll()) {
             scrolled = true;
@@ -542,6 +594,20 @@ void Element::applyScroll(ScrollState& scrollState)
         document().frame()->view()->setWasScrolledByUser(true);
 };
 
+void Element::callApplyScroll(ScrollState& scrollState)
+{
+    if (!hasRareData() || !elementRareData()->getApplyScroll()) {
+        nativeApplyScroll(scrollState);
+    } else {
+        ScrollStateCallback& callback = *elementRareData()->getApplyScroll();
+        if (callback.nativeScrollBehavior() == PerformAfterNativeScroll)
+            nativeApplyScroll(scrollState);
+        callback.handleEvent(&scrollState);
+        if (callback.nativeScrollBehavior() == PerformBeforeNativeScroll)
+            nativeApplyScroll(scrollState);
+    }
+};
+
 static float localZoomForLayoutObject(LayoutObject& layoutObject)
 {
     // FIXME: This does the wrong thing if two opposing zooms are in effect and canceled each