Fix wheel event dispatch logic to fallback to document when hit-test fails

Source/core/input/EventHandler.cpp

Index: Source/core/input/EventHandler.cpp
diff --git a/Source/core/input/EventHandler.cpp b/Source/core/input/EventHandler.cpp
index 19698b6bf5a0b587896378adc6a5058273c8515d..0f9dd0cf3ff0750fadb0c22a50f7edc318535ea2 100644
--- a/Source/core/input/EventHandler.cpp
+++ b/Source/core/input/EventHandler.cpp
@@ -1725,7 +1725,9 @@ bool EventHandler::handleWheelEvent(const PlatformWheelEvent& event)
 
     LayoutPoint vPoint = view->rootFrameToContents(event.position());
 
-    HitTestRequest request(HitTestRequest::ReadOnly);
+    // Pass Active to ensure that hit-test result in current document if otherwise empty
+    // TODO(majidvp): Avoid using Active to trigger hit-testing fallback. See http://crbug.com/505825
+    HitTestRequest request(HitTestRequest::ReadOnly | HitTestRequest::Active);

[Rick Byers, 2015/06/30 20:14:49]

I assume you've done a search to verify that this won't trigger other intended 
side effects inside hit testing somewhere, right?

HitTestRequest::Move would be less of a lie if that part of the hack would work
just as well for you (Active really means a mouse button is down).

[majidvp, 2015/06/30 22:48:32]

Yes I have. It shouldn't have any other side effects when used in combination
with ReadOnly. 
The only other effect of Active is to update hover and active state but that
does not kicked in when ReadOnly is present. This is why "ReadOnly | Active" is
used for this in few other places without causing side-effects.

Move may also work but additionally it requires the point to be in the frame
visible area rect. This should be fine for any user input generated events but
may be problematic for script generated events. I have a test case
specifically for mouse events that are outside visible frame rect which fails
when Move is used.

[Rick Byers, 2015/07/01 13:41:03]

Alright, good enough for a temporary hack.  Thanks!

     HitTestResult result(request, vPoint);
     doc->layoutView()->hitTest(result);