Fix wheel scrolling over scrollbar not scrolling page.

third_party/WebKit/Source/core/input/EventHandler.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 1780 matching lines @@
 
     HitTestRequest request(HitTestRequest::ReadOnly);
     HitTestResult result(request, vPoint);
     doc->layoutView()->hitTest(result);
 
     Node* node = result.innerNode();
     // Wheel events should not dispatch to text nodes.
     if (node && node->isTextNode())
         node = FlatTreeTraversal::parent(*node);
 
+    // If we're over a scrollbar, scroll the document.

[jbroman, 2016/03/16 15:41:00]

Just the (root?) frame scrollbars, right? Presumably hitting an overflow
scrollbar shouldn't scroll the document.

(I'm not familiar with what HitTestResult::innerNode will be in such cases, so I
don't know if this is just a question about the comment, or also the code.)

[bokan, 2016/03/16 18:01:45]

Yah, if it's over an overflow div innerNode will have the associated Node. I've
updated the comment.

+    if (!node && result.scrollbar())
+        node = doc->documentElement();
+
     bool sendDOMEvent = true;
     LocalFrame* subframe = subframeForTargetNode(node);
     if (subframe) {
         WebInputEventResult result = subframe->eventHandler().handleWheelEvent(event);
         if (result != WebInputEventResult::NotHandled) {
             setFrameWasScrolledByUser();
             return result;
         }
         // TODO(dtapuska): Remove this once wheel gesture scroll has
         // been enabled everywhere; as we can just return early.
@@ skipping 2158 matching lines @@
 PlatformEvent::Modifiers EventHandler::accessKeyModifiers()
 {
 #if OS(MACOSX)
     return static_cast<PlatformEvent::Modifiers>(PlatformEvent::CtrlKey | PlatformEvent::AltKey);
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace blink