Straighten out SkPicture::AccelData APIs.

Straighten out SkPicture::AccelData APIs.

Must have been we needed them to be weird (mutable, const setter) before.
It doesn't look like that's necessary now... we can just pass it to the
constructor.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/2420e10d5a86da1964a05a749ab9bb625ae9f13e

[mtklein_C, 2015-04-29 14:24:53]

mtklein@chromium.org changed reviewers:
+ robertphillips@google.com

[mtklein_C, 2015-04-29 14:26:07]

The CQ bit was checked by mtklein@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-04-29 14:26:14]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1112833003/1

[commit-bot: I haz the power, 2015-04-29 14:32:05]

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

[commit-bot: I haz the power, 2015-04-29 14:32:05]

Dry run: This issue passed the CQ dry run.

[reed1, 2015-04-29 14:58:28]

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

[reed1, 2015-04-29 14:58:28]

api lgtm

[robertphillips, 2015-04-29 15:15:33]

lgtm

[mtklein, 2015-04-29 15:16:28]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-04-29 15:16:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1112833003/1

[commit-bot: I haz the power, 2015-04-29 15:16:53]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/2420e10d5a86da1964a05a749ab9bb625ae9f13e