Handle rewinds in SkBmpCodec.

Handle rewinds in SkBmpCodec.

Factor our BMP code for reading the header, and call it after a rewind.

BUG=skia:3257
Committed: https://skia.googlesource.com/skia/+/79e378d9b78c3db28eb97ab9adecb5bfddbf52d8

[scroggo, 2015-04-01 14:05:36]

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

[msarett, 2015-04-01 14:12:07]

lgtm

Thanks for crossing this off my list of things to do!

[scroggo, 2015-04-01 14:16:19]

The CQ bit was checked by scroggo@google.com

[commit-bot: I haz the power, 2015-04-01 14:16:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1057483003/1

[commit-bot: I haz the power, 2015-04-01 14:17:41]

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

[commit-bot: I haz the power, 2015-04-01 14:17:42]

Try jobs failed on following builders:
  Build-Ubuntu-GCC-x86_64-Release-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-x86...)

[scroggo, 2015-04-01 14:32:14]

The CQ bit was checked by scroggo@google.com

[scroggo, 2015-04-01 14:32:14]

The patchset sent to the CQ was uploaded after l-g-t-m from msarett@google.com
Link to the patchset: https://codereview.chromium.org/1057483003/#ps20001
(title: "Initialize codec to defeat warning.")

[commit-bot: I haz the power, 2015-04-01 14:32:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1057483003/20001

[commit-bot: I haz the power, 2015-04-01 14:39:43]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/79e378d9b78c3db28eb97ab9adecb5bfddbf52d8