Prevent default actions for JS-generated mouse events other than click

Source/core/events/MouseEvent.cpp

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 242 matching lines @@
 
 MouseEvent& MouseEventDispatchMediator::event() const
 {
     return toMouseEvent(EventDispatchMediator::event());
 }
 
 bool MouseEventDispatchMediator::dispatchEvent(EventDispatcher& dispatcher) const
 {
     if (isSyntheticMouseEvent()) {
         event().eventPath().adjustForRelatedTarget(dispatcher.node(), event().relatedTarget());
+        event().markAsSynthetic();
         return dispatcher.dispatch();
     }
 
     if (isDisabledFormControl(&dispatcher.node()))
         return false;
 
     if (event().type().isEmpty())
         return true; // Shouldn't happen.
 
     ASSERT(!event().target() || event().target() != event().relatedTarget());
@@ skipping 17 matching lines @@
         event().button(), relatedTarget, event().buttons());
     if (event().defaultHandled())
         doubleClickEvent->setDefaultHandled();
     EventDispatcher::dispatchEvent(dispatcher.node(), MouseEventDispatchMediator::create(doubleClickEvent));
     if (doubleClickEvent->defaultHandled() || doubleClickEvent->defaultPrevented())
         return false;
     return !swallowEvent;
 }
 
 } // namespace blink