WebGL specifies a maximum token size of 256 characters, while
ES3 specifies 1024 characters. We can determine the proper max
size to support from the spec.

BUG=angle:550
Change-Id: I6aeabe8af3b6184a27b456248ce2f84f361b76e4
Reviewed-on: https://chromium-review.googlesource.com/186973Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>