Don't allow drags to start after a mouse press that creates a context menu
https://bugs.webkit.org/show_bug.cgi?id=112079

Reviewed by Tony Chang.

.:

* ManualTests/context-menu-during-drag-selection.html: Added.

Source/WebCore:

This appears to be the intent of the original code anyway (the comments in the corresponding
context menu handlers indicate that they set m_mousePressed to false in order to suppress
drags from starting). Since exact platform behavior differs quite a bit in this area, this
will also make the behavior more consistent across different WebKit implementations.

Manually testable using context-menu-during-drag-selection.html.

* page/EventHandler.cpp:
(WebCore::EventHandler::handleMouseDraggedEvent):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146784 268f45cc-cd09-0410-ab3c-d52691b4dbfc