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 71191c2d41e13f567b68072831047999af2ca051..f9ac92895cf5069982d831c00d16cc7e4634ace0 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -30,6 +30,8 @@
 #include "bindings/core/v8/Dictionary.h"
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
+#include "bindings/core/v8/ScriptFunctionCall.h"
+#include "bindings/core/v8/ToV8.h"
 #include "bindings/core/v8/V8DOMWrapper.h"
 #include "bindings/core/v8/V8PerContextData.h"
 #include "core/CSSValueKeywords.h"
@@ -489,7 +491,38 @@ void Element::scrollIntoViewIfNeeded(bool centerIfNeeded)
         layoutObject()->scrollRectToVisible(bounds, ScrollAlignment::alignToEdgeIfNeeded, ScrollAlignment::alignToEdgeIfNeeded);
 }
 
-void Element::distributeScroll(ScrollState& scrollState)
+// Returns true iff a V8 method existed and was called.
+static bool callScrollCustomizationV8Method(Element* element,
+    ScrollState& scrollState, String methodName)
+{
+    ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
+
+    LocalFrame* frame = element->document().frame();
+    if (!frame)
+        return false;
+    ScriptState* scriptState = ScriptState::forMainWorld(frame);
+    ScriptState::Scope scope(scriptState);
+
+    v8::Handle<v8::Object> creationContext = scriptState->context()->Global();
+    ScriptValue thisWrapper = ScriptValue(scriptState, toV8(element, creationContext, scriptState->isolate()));
+    ScriptValue scrollStateWrapper = ScriptValue(scriptState, toV8(&scrollState, creationContext, scriptState->isolate()));
+
+    v8::Handle<v8::Object> thisObject = v8::Handle<v8::Object>::Cast(thisWrapper.v8Value());
+    v8::Local<v8::Value> functionValue = thisObject->Get(v8String(scriptState->isolate(), methodName));
+    ASSERT(functionValue->IsFunction());
+    v8::Local<v8::Function> function = v8::Local<v8::Function>::Cast(functionValue);
+
+    // Native methods should avoid the performance overhead of a v8 method call.
+    if (function->ScriptId() == v8::UnboundScript::kNoScriptId)
+        return false;
+
+    ScriptFunctionCall functionCall(thisWrapper, methodName);
+    functionCall.appendArgument(scrollStateWrapper);
+    functionCall.call();
+    return true;
+}
+
+void Element::distributeScrollNative(ScrollState& scrollState)
 {
     ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
     if (scrollState.fullyConsumed())
@@ -509,13 +542,25 @@ 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 (!callScrollCustomizationV8Method(this, scrollState, "distributeScroll"))
+        distributeScrollNative(scrollState);
+};
+
+void Element::distributeScroll(ScrollState* scrollState)
+{
+    ASSERT(scrollState);
+    distributeScrollNative(*scrollState);
+}
+
+void Element::applyScrollNative(ScrollState& scrollState)
 {
     ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
     if (scrollState.fullyConsumed())
@@ -561,6 +606,18 @@ void Element::applyScroll(ScrollState& scrollState)
         document().frame()->view()->setWasScrolledByUser(true);
 };
 
+void Element::callApplyScroll(ScrollState& scrollState)
+{
+    if (!callScrollCustomizationV8Method(this, scrollState, "applyScroll"))
+        applyScrollNative(scrollState);
+};
+
+void Element::applyScroll(ScrollState* scrollState)
+{
+    ASSERT(scrollState);
+    applyScrollNative(*scrollState);
+}
+
 static float localZoomForRenderer(LayoutObject& renderer)
 {
     // FIXME: This does the wrong thing if two opposing zooms are in effect and canceled each