ServiceWorker: Database functions should return status code instead of boolean

ServiceWorker: Database functions should return status code instead of boolean

Currently to get an error reason (not found, database corruption, ...), we have
to check is_disabled() and was_corruption_detected() after database operations.
It's a bit messy for the storage class because these functions must be called on
the database task runner.

This change makes database functions return status code instead of boolean.
Other remaining functions will be modified like this in following CLs.


BUG=372704
TEST=should pass all existing tests (no behavioral changes)

[nhiroki, 2014-05-13 08:28:41]

michaeln@ (or anyone), can you review this? Thanks!

[jsbell, 2014-05-13 11:22:06]

lgtm

[nhiroki, 2014-05-13 12:18:01]

The CQ bit was checked by nhiroki@chromium.org

[nhiroki, 2014-05-13 12:18:06]

The CQ bit was unchecked by nhiroki@chromium.org

[commit-bot: I haz the power, 2014-05-13 12:18:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nhiroki@chromium.org/275103004/1

[michaeln, 2014-05-13 20:38:47]

lgtm2

[nhiroki, 2014-05-13 23:18:53]

The CQ bit was checked by nhiroki@chromium.org

[commit-bot: I haz the power, 2014-05-13 23:20:22]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nhiroki@chromium.org/275103004/1

[commit-bot: I haz the power, 2014-05-13 23:24:37]

Change committed as 270240