Refactoring patch only. Reduces the number of parameters we need to
pass around in internal functions. Clears the way for future
optimization work.

BUG=angleproject:959

Change-Id: Ic98ab5a07189eaa053dffce994546666bb07cede
Reviewed-on: https://chromium-review.googlesource.com/277281Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>