Fix counting of the new platform methods. The context pointer was throwing off the count by one. Also change the type to void * for ease of use. BUG=angleproject:1892 BUG=chromium:678870 Change-Id: Iffac667f0aa896d9247e9ffddfeb3bc447a9692f Reviewed-on: https://chromium-review.googlesource.com/441931 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>