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>