When a enum is given that is not a BACK, NONE, or COLOR_ATTACHMENTi where
i ranges from 0 to MAX_COLOR_ATTACHMENT, an INVALID_ENUM should be
returned rather than an INVALID_OPERATION.

BUG=angleproject:1148

Change-Id: I3663f897face14f6ba46a15fb982efda6f4f4b05
Reviewed-on: https://chromium-review.googlesource.com/299312
Tryjob-Request: Dian Xiang <dianx@google.com>
Tested-by: Dian Xiang <dianx@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>