Reviewed by Maciej Stachowiak.

    Reviewed by Maciej Stachowiak.

        - fix <rdar://problem/5596160> fast/events/objc-event-api.html fails when run alone (or first)

        * WebView/WebHTMLView.mm:
        (-[WebHTMLView setDataSource:]): This method calls addMouseMovedObserver
        because addMouseMovedObserver returns early if the dataSource
        is not nil. But if the dataSource is already set (which happens when
        a WebHTMLView is being reused) then addMouseMovedObserver must not
        be called again.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@28104 268f45cc-cd09-0410-ab3c-d52691b4dbfc