Treat a GIF with no color table as transparent

Treat a GIF with no color table as transparent

When checking to see whether a GIF has transparency to determine its
alpha type, treat an empty color table as having alpha, since we
will draw it as a transparent image.

(This is a separate bug from skbug.com/5883, but the image I used to
verify that bug was drawn to 565 as black. The fix is to not support
565 in that case, by changing its recommended alpha type.)

BUG=skia:5883
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2461813002

Committed: https://skia.googlesource.com/skia/+/2f7068aec9906168b3c142b5057e098114376cc9

[scroggo_chromium, 2016-10-28 21:27:55]

Description was changed from

==========
Treat a GIF with no color table as transparent

When checking to see whether a GIF has transparency to determine its
alpha type, treat an empty color table as having alpha, since we
will draw it as a transparent image.

(This is a separate bug from skbug.com/5883, but the image I used to
verify that bug was drawn to 565 as black. The fix is to not support
565 in that case, by changing its recommended alpha type.)

BUG=skia:5883
==========

to

==========
Treat a GIF with no color table as transparent

When checking to see whether a GIF has transparency to determine its
alpha type, treat an empty color table as having alpha, since we
will draw it as a transparent image.

(This is a separate bug from skbug.com/5883, but the image I used to
verify that bug was drawn to 565 as black. The fix is to not support
565 in that case, by changing its recommended alpha type.)

BUG=skia:5883
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2461813002
==========

[scroggo, 2016-10-28 21:28:18]

scroggo@google.com changed reviewers:
+ joostouwerling@google.com, msarett@google.com, scroggo@google.com

[msarett, 2016-10-28 21:50:58]

lgtm

[scroggo, 2016-10-31 11:25:16]

The CQ bit was checked by scroggo@google.com

[commit-bot: I haz the power, 2016-10-31 11:25:27]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-31 11:45:13]

Description was changed from

==========
Treat a GIF with no color table as transparent

When checking to see whether a GIF has transparency to determine its
alpha type, treat an empty color table as having alpha, since we
will draw it as a transparent image.

(This is a separate bug from skbug.com/5883, but the image I used to
verify that bug was drawn to 565 as black. The fix is to not support
565 in that case, by changing its recommended alpha type.)

BUG=skia:5883
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2461813002
==========

to

==========
Treat a GIF with no color table as transparent

When checking to see whether a GIF has transparency to determine its
alpha type, treat an empty color table as having alpha, since we
will draw it as a transparent image.

(This is a separate bug from skbug.com/5883, but the image I used to
verify that bug was drawn to 565 as black. The fix is to not support
565 in that case, by changing its recommended alpha type.)

BUG=skia:5883
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2461813002

Committed:
https://skia.googlesource.com/skia/+/2f7068aec9906168b3c142b5057e098114376cc9
==========

[commit-bot: I haz the power, 2016-10-31 11:45:14]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/2f7068aec9906168b3c142b5057e098114376cc9