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 9b72286ae6c846cfcce1055b957dd715018fe121..f635b5d48fe2260f689530a8f06435e86abaa3c7 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -112,7 +112,9 @@
 #include "core/page/Page.h"
 #include "core/page/PointerLockController.h"
 #include "core/page/SpatialNavigation.h"
+#include "core/page/scrolling/ScrollCustomizationCallbacks.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"
@@ -128,6 +130,25 @@
 
 namespace blink {
 
+namespace {
+
+// We need to retain the scroll customization callbacks until the element
+// they're associated with is destroyed. It would be simplest if the callbacks
+// could be stored in ElementRareData, but we can't afford the space
+// increase. Instead, keep the scroll customization callbacks here. The other
+// option would be to store these callbacks on the FrameHost or document, but
+// that necessitates a bunch more logic for transferring the callbacks between
+// FrameHosts when elements are moved around.
+ScrollCustomizationCallbacks& scrollCustomizationCallbacks()
+{
+    ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
+    DEFINE_STATIC_LOCAL(Persistent<ScrollCustomizationCallbacks>,
+        scrollCustomizationCallbacks, (new ScrollCustomizationCallbacks()));
+    return *scrollCustomizationCallbacks;
+}
+
+} // namespace
+
 using namespace HTMLNames;
 using namespace XMLNames;
 
@@ -155,6 +176,9 @@ Element::~Element()
     if (isCustomElement())
         CustomElement::wasDestroyed(this);
 
+    if (RuntimeEnabledFeatures::scrollCustomizationEnabled())
+        scrollCustomizationCallbacks().removeCallbacksForElement(this);
+
     // With Oilpan, either the Element has been removed from the Document
     // or the Document is dead as well. If the Element has been removed from
     // the Document the element has already been removed from the pending
@@ -470,7 +494,19 @@ void Element::scrollIntoViewIfNeeded(bool centerIfNeeded)
         layoutObject()->scrollRectToVisible(bounds, ScrollAlignment::alignToEdgeIfNeeded, ScrollAlignment::alignToEdgeIfNeeded);
 }
 
-void Element::distributeScroll(ScrollState& scrollState)
+void Element::setDistributeScroll(ScrollStateCallback* scrollStateCallback, String nativeScrollBehavior)
+{
+    scrollStateCallback->setNativeScrollBehavior(ScrollStateCallback::toNativeScrollBehavior(nativeScrollBehavior));
+    scrollCustomizationCallbacks().setDistributeScroll(this, scrollStateCallback);
+}
+
+void Element::setApplyScroll(ScrollStateCallback* scrollStateCallback, String nativeScrollBehavior)
+{
+    scrollStateCallback->setNativeScrollBehavior(ScrollStateCallback::toNativeScrollBehavior(nativeScrollBehavior));
+    scrollCustomizationCallbacks().setApplyScroll(this, scrollStateCallback);
+}
+
+void Element::nativeDistributeScroll(ScrollState& scrollState)
 {
     ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
     if (scrollState.fullyConsumed())
@@ -490,13 +526,27 @@ 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)
+{
+    ScrollStateCallback* callback = scrollCustomizationCallbacks().getDistributeScroll(this);
+    if (!callback) {
+        nativeDistributeScroll(scrollState);
+    } else {
+        if (callback->nativeScrollBehavior() == NativeScrollBehavior::PerformAfterNativeScroll)
+            nativeDistributeScroll(scrollState);
+        callback->handleEvent(&scrollState);
+        if (callback->nativeScrollBehavior() == NativeScrollBehavior::PerformBeforeNativeScroll)
+            nativeDistributeScroll(scrollState);
+    }
+};
+
+void Element::nativeApplyScroll(ScrollState& scrollState)
 {
     ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
     if (scrollState.fullyConsumed())
@@ -506,8 +556,11 @@ 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 viewport.
+    if (this == document().scrollingElement()) {
         FloatSize delta(deltaX, deltaY);
         if (document().frame()->applyScrollDelta(delta, scrollState.isBeginning()).didScroll()) {
             scrolled = true;
@@ -542,6 +595,20 @@ void Element::applyScroll(ScrollState& scrollState)
         document().frame()->view()->setWasScrolledByUser(true);
 };
 
+void Element::callApplyScroll(ScrollState& scrollState)
+{
+    ScrollStateCallback* callback = scrollCustomizationCallbacks().getApplyScroll(this);
+    if (!callback) {
+        nativeApplyScroll(scrollState);
+    } else {
+        if (callback->nativeScrollBehavior() == NativeScrollBehavior::PerformAfterNativeScroll)
+            nativeApplyScroll(scrollState);
+        callback->handleEvent(&scrollState);
+        if (callback->nativeScrollBehavior() == 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