Drive-by change: Add helper method for reporting naming
convention errors and refactor existing call sites.

R=tebbi@chromium.org

Bug: v8:7793
Change-Id: I7315b935229ffb7557fa55ebcb222fc91124aab7
Reviewed-on: https://chromium-review.googlesource.com/1223831Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Simon Zünd <szuend@google.com>
Cr-Commit-Position: refs/heads/master@{#55847}