Avoid a CHECK in ExtensionActionStorageManager::ReadFromStorage if an extension

Avoid a CHECK in ExtensionActionStorageManager::ReadFromStorage if an extension
has a browser action which it starts reading from storage on startup, but then
it's updated to a new version with no browser action before the callback comes
back.

A better way to fix it would be to block the update until the extension is
"started", but we need better infrastructure to do that.

BUG=349371
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=255201

[Matt Perry, 2014-03-05 19:07:30]

lgtm

[Jeffrey Yasskin, 2014-03-05 19:07:53]

The CQ bit was checked by jyasskin@chromium.org

[commit-bot: I haz the power, 2014-03-05 19:08:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jyasskin@chromium.org/187323007/1

[commit-bot: I haz the power, 2014-03-05 20:35:13]

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

[commit-bot: I haz the power, 2014-03-05 20:35:14]

Retried try job too often on win_rel for step(s) unit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[Jeffrey Yasskin, 2014-03-05 21:16:39]

The CQ bit was checked by jyasskin@chromium.org

[commit-bot: I haz the power, 2014-03-05 21:20:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jyasskin@chromium.org/187323007/1

[commit-bot: I haz the power, 2014-03-06 00:01:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jyasskin@chromium.org/187323007/1

[commit-bot: I haz the power, 2014-03-06 01:20:24]

Change committed as 255201