Move user_story.shared_user_story_state to story.shared_state

Move user_story.shared_user_story_state to story.shared_state

BUG=465594
Committed: https://crrev.com/6d62551b30fb6cf12a2a50c1ab4feb08c386a2ba
Cr-Commit-Position: refs/heads/master@{#327596}

[aiolos (Not reviewing), 2015-04-29 20:51:46]

aiolos@chromium.org changed reviewers:
+ dtu@chromium.org, nednguyen@google.com

[aiolos (Not reviewing), 2015-04-29 20:54:00]

aiolos@chromium.org changed reviewers:
+ sullivan@chromium.org

[aiolos (Not reviewing), 2015-04-29 20:54:00]

Per discussion with Ned offline, I'm not providing a stub for the old
shared_user_story_state. I don't *think* anyone is subclassing this directly
yet. (And they are instead using shared_page_state or shared_app_state.)

[nednguyen, 2015-04-29 20:57:06]

lgtm

[aiolos (Not reviewing), 2015-04-29 21:52:25]

The CQ bit was checked by aiolos@chromium.org

[commit-bot: I haz the power, 2015-04-29 21:54:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1108993004/1

[commit-bot: I haz the power, 2015-04-29 22:07:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-29 22:07:52]

Patchset 1 (id:??) landed as
https://crrev.com/6d62551b30fb6cf12a2a50c1ab4feb08c386a2ba
Cr-Commit-Position: refs/heads/master@{#327596}