This caused the context to be current from ANGLE's point of view while
it wasn't from the driver's point of view.

BUG=angleproject:892

Change-Id: I0719b4702721916e9eb3a9f4cafc7a86dbc7a625
Reviewed-on: https://chromium-review.googlesource.com/284871Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>