Also moves some code to the cpp.

Bug: angleproject:2747
Change-Id: I38468e6276d52d11d5751df6917c66f15ae61246
Reviewed-on: https://chromium-review.googlesource.com/1163822
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>