Introduce CurrentJavascriptContext to provide Browser/Frame objects to python funcs called from js

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When python function is called from javascript we don't know from which browser 
or frame it originates. We should pass the context as a first argument, a frame 
or both, browser and frame. Passing only frame would be enough if we had 
!GetBrowser() method in Frame object. Or should we pass "context" dictionary 
with "browser" and "frame" keys?

Original issue reported on code.google.com by czarek.t...@gmail.com on 28 Nov 2012 at 3:25