WebGL: Validate shader entry point names do not contain invalid characters. Section 6.20 of the WebGL spec states that all shader-related entry points that accept strings must validate that the string does not contain characters that are not valid in ESSL. TEST=conformance/misc/invalid-passed-params BUG=2016 Change-Id: I220d9dd79c4b0e8e0195277093268b9e1e66f9d9 Reviewed-on: https://chromium-review.googlesource.com/519445 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>