Create render view for extensions on Linux.

Create render view for extensions on Linux.

Now when an extension is loaded, you will see its entry in the task manager.
However, on the shelf there is still only a placeholder label (I have to
work on setting proper size for the render widget).

TEST=none
http://crbug.com/16759

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=21908

[Paweł Hajdan Jr., 2009-07-28 19:07:47]

Please review:

erg: GTK parts
aa: extension parts

[Elliot Glaysher, 2009-07-28 19:23:58]

GTK parts LGTM

[Aaron Boodman, 2009-07-28 22:38:28]

Other parts LGTM