[vtkusers] vtk + NPAPI + MAC

[Vincenzo Farruggia]

Hi all,
I'm porting a standalone vtk app to browser plugin, but I have some troubles 
with render window initialization.
I can get from browser a CGContext or a CALayer but I can't take a 
NSWindow/NSView where attach vtkCocoaRenderWindow/vtkCocoaGLView

Can you give some advice? 
I even think to use vtkOpenGLRenderWindow but I haven't found anything how to 
use and in api doc I found that this class shouldn't be used directly.

Thanks all
Vincent