Ignore unsupported disposal methods when decoding GIF

Ignore unsupported disposal methods when decoding GIF

Avoid assertion failures about invalid disposal methods by ignoring
unsupported values when decoding GIF.

The bug is caused by some GIF images containing frames with disposal
method 5. Don't know what the author wanted.

BUG=302034
R=aelias@chromium.org, pkasting@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=158769

[Xianzhu, 2013-10-01 03:37:41]

Perhaps it'd be better to print some warning messages, but I'm ignoring the
unsupported values just like other places in GIFImageDecoder/GIFImageReader
handling similar situations. Not returning false to keep compatibility with
existing behavior of release-build.

[Peter Kasting, 2013-10-01 20:55:04]

PLease add a test for this.

LGTM once that's done.

[Xianzhu, 2013-10-02 23:48:48]

On 2013/10/01 20:55:04, Peter Kasting wrote:
> PLease add a test for this.

Done.

[commit-bot: I haz the power, 2013-10-02 23:51:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/25422003/5001

[commit-bot: I haz the power, 2013-10-03 00:08:03]

Retried try job too often on blink_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=blink_pres...

[Xianzhu, 2013-10-03 00:13:14]

+aelias as OWNER of Source/web/tests/data

[aelias_OOO_until_Jul13, 2013-10-03 00:19:18]

lgtm

[commit-bot: I haz the power, 2013-10-03 00:20:22]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/25422003/5001

[commit-bot: I haz the power, 2013-10-03 00:40:51]

Retried try job too often on blink_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=blink_pres...

[Xianzhu, 2013-10-03 01:03:28]

Committed patchset #2 manually as r158769 (presubmit successful).