See section 2.2 of the EGL 1.5 specification.

BUG=angleproject:892

Change-Id: I2a43260e53cb045b2e06b0e50915e228cec96f33
Reviewed-on: https://chromium-review.googlesource.com/272370Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>