Avoid dec = -dec overflow when appending most negative signed integers.

Avoid dec = -dec overflow when appending most negative signed integers.

BUG=skia:3096
Committed: https://skia.googlesource.com/skia/+/225fb98e1e321fa80e3457fafcd5d1fa14d9f8c3

[mtklein, 2014-11-05 17:04:40]

mtklein@google.com changed reviewers:
+ mtklein@google.com, reed@google.com

[mtklein, 2014-11-05 17:07:33]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-05 17:08:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/700953003/1

[commit-bot: I haz the power, 2014-11-05 17:08:40]

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 2014-11-05 23:08 UTC

[commit-bot: I haz the power, 2014-11-05 17:15:45]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-11-05 17:15:46]

Try jobs failed on following builders:
  Build-Win-VS2013-x86-Debug-Trybot on client.skia.compile
(http://build.chromium.org/p/client.skia.compile/builders/Build-Win-VS2013-x86...)

[mtklein, 2014-11-05 17:21:16]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-05 17:21:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/700953003/20001

[commit-bot: I haz the power, 2014-11-05 17:21:57]

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 2014-11-05 23:21 UTC

[reed1, 2014-11-05 19:34:30]

wacky

lgtm

[commit-bot: I haz the power, 2014-11-05 19:35:27]

Committed patchset #2 (id:20001) as 225fb98e1e321fa80e3457fafcd5d1fa14d9f8c3