chromectrl: a new timer for message loop processing is created for each ChromeWindow instance

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There should be only one global timer running. In the wxpython.py example the 
timer is created and destroyed in wx.App. But in chromectrl it is created for 
each chrome window. Creating multiple timers that call CefMessageLoopWork 
simultaneously might result in performance penalties and an undefined behavior.

Original issue reported on code.google.com by czarek.t...@gmail.com on 30 Jul 2014 at 8:11