Add default compiler options to WebGL shaders. Enforces default compiler options when compiling WebGL compatible shaders. BUG=angleproject:1616 Change-Id: I18490db68b29981fab4817bdd61727752cf50997 Reviewed-on: https://chromium-review.googlesource.com/409016 Commit-Queue: Bryan Bernhart <bryan.bernhart@intel.com> Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>