Also fixes a few instances of variable shadowing in the code.

Bug: angleproject:6148
Change-Id: Ic51d722a3f953f246f51af6d74abb302f832cf44
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3014875Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>