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 8a3c55dc5d609d6304bf5fcb54fc2baa967b7c1f..09b3732fa8e3d9fbec6a1e10e32fb450d8d2301b 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"
@@ -477,7 +479,38 @@ 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);

[haraken, 2015/06/09 00:07:13]

Why can we assume the main world?

[tdresser, 2015/06/09 14:27:42]

We're okay if scroll customization methods can only be assigned from the main
world.

My understanding is that currently, if you assign a scroll customization method
from a world other than the main world, this code will pay no attention to it.
Is that correct?

[haraken, 2015/06/09 15:16:38]

That is not OK. Unless you have a strong reason to do so, we should support the
Web API in isolated worlds as well.
If an isolated world assigns a scroll customization method, it will install the
method on the main world -- which is not correct.

Assuming that callScrollCustomizationV8Method is called from only JavaScript, I
think you can use:

  ScriptState* scriptState = ScriptState::current(toIsolate(frame));

which will give you the ScriptState of the JS that called the
callScrollCustomizationV8Method.

(However, I'd strongly recommend using a callback interface because that's a
standard way to handle this kind of situation in a safe manner.)

[tdresser, 2015/06/26 14:53:15]

callScrollCustomizationV8Method is never called from JavaScript.

+    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);

[haraken, 2015/06/09 00:07:12]

ScriptFunctionCall is an abstraction for devtools. Can we use
V8ScriptRunner::callFunction?

[tdresser, 2015/06/09 14:27:42]

Done.

+    functionCall.appendArgument(scrollStateWrapper);
+    functionCall.call();
+    return true;
+}
+
+void Element::distributeScrollNative(ScrollState& scrollState)
 {
     ASSERT(RuntimeEnabledFeatures::scrollCustomizationEnabled());
     if (scrollState.fullyConsumed())
@@ -497,15 +530,29 @@ 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());
+    document().updateLayoutIgnorePendingStylesheets();
+
     if (scrollState.fullyConsumed())
         return;
 
@@ -513,8 +560,8 @@ 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()) {
+    // Handle the scrollingElement separately, as it scrolls the FrameView.
+    if (this == document().scrollingElement()) {
         FloatSize delta(deltaX, deltaY);
         if (document().frame()->applyScrollDelta(delta, scrollState.isBeginning())) {
             scrolled = true;
@@ -549,6 +596,18 @@ 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 localZoomForLayoutObject(LayoutObject& layoutObject)
 {
     // FIXME: This does the wrong thing if two opposing zooms are in effect and canceled each