Otherwise glGetString(GL_RENDERER) returns "ANGLE" and doesn't provide
information on the vendor.

BUG=angleproject:892

Change-Id: I01899ca78656aaa8db860829c78bf3c61c355eae
Reviewed-on: https://chromium-review.googlesource.com/284051Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>