Fix unit test crash caused by OSMesa not supporting rendering to GL_ALPHA8

Fix unit test crash caused by OSMesa not supporting rendering to GL_ALPHA8
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1947373003

Committed: https://skia.googlesource.com/skia/+/4017007b288087c07c596baa9fe8ecf485bca1c3

[bsalomon, 2016-05-05 21:24:02]

Description was changed from

==========
Fix unit test crash caused by OSMesa not supporting rendering to GL_ALPHA8
==========

to

==========
Fix unit test crash caused by OSMesa not supporting rendering to GL_ALPHA8
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

[bsalomon, 2016-05-05 21:24:59]

bsalomon@google.com changed reviewers:
+ robertphillips@google.com

[bsalomon, 2016-05-05 21:25:07]

The CQ bit was checked by bsalomon@google.com

[commit-bot: I haz the power, 2016-05-05 21:25:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1947373003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1947373003/1

[commit-bot: I haz the power, 2016-05-05 21:25:11]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2016-05-06 03:25 UTC

[robertphillips, 2016-05-05 21:33:55]

lgtm

[commit-bot: I haz the power, 2016-05-05 21:40:06]

Description was changed from

==========
Fix unit test crash caused by OSMesa not supporting rendering to GL_ALPHA8
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

to

==========
Fix unit test crash caused by OSMesa not supporting rendering to GL_ALPHA8
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...

Committed:
https://skia.googlesource.com/skia/+/4017007b288087c07c596baa9fe8ecf485bca1c3
==========

[commit-bot: I haz the power, 2016-05-05 21:40:07]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/4017007b288087c07c596baa9fe8ecf485bca1c3