Validate precision in uniform blocks for WebGL. In WebGL mode turn on checking that precision qualifiers match in corresponding vertex/fragment uniform blocks. Add test for this behavior. BUG=angleproject:2015 Change-Id: Ie035138e8c46e430bdcf8fb5bbc3e0a3ab7d6391 Reviewed-on: https://chromium-review.googlesource.com/517724 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>