Fix WebGL validation of characters in shader source strings. Shader source strings are allowed invalid ESSL characters when they are in comments. Added a simple comment parser to determine which characters should be validated. BUG=angleproject:2093 Change-Id: If78a4ecbd61f1700fc18dcb844f3de03314a6a39 Reviewed-on: https://chromium-review.googlesource.com/578567 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>