glTexStorage requires sized formats, ensure that we're following that rule

In some situations (at least ANGLE ES3), we were passing GL_BGRA, rather
than GL_BGRA8.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2336613002

Review-Url: https://codereview.chromium.org/2336613002
1 file changed