[WebKit2] Add CoordinatedGraphics to the list of platforms in generate-forwarding-headers.pl
https://bugs.webkit.org/show_bug.cgi?id=115098

Patch by Carlos Garcia Campos <cgarcia@igalia.com> on 2013-04-24
Reviewed by Martin Robinson.

r148963 introduced a new WKView.h header in a directory not listed
as a platform prefix in generate-forwarding-headers.pl.

* Scripts/generate-forwarding-headers.pl: Replace unused chromium
plaform prefix with CoordinatedGraphics that is used now.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149036 268f45cc-cd09-0410-ab3c-d52691b4dbfc