We neglected to update the text of the guards when we renamed the
file from Uniform.h to ShaderVariable.h.

BUG=angle:533

Change-Id: I59969113536b69a418cf233ef0d7dd797e666ea9
Reviewed-on: https://chromium-review.googlesource.com/180978Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Commit-Queue: Nicolas Capens <nicolascapens@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>