Support PolicyWatcher with custom loader for testing

Support PolicyWatcher with custom loader for testing

PolicyWatcher::Create automatically creates an underlying
AsyncPolicyLoader corresponding to the policy storage location of the
current platform. This commit adds an alternative constructor,
CreateFromPolicyLoaderForTesting, which allows a custom
AsyncPolicyLoader to be specified to allow testing other components with
different policy configurations.

Review-Url: https://codereview.chromium.org/2764333003
Cr-Commit-Position: refs/heads/master@{#460592}
Committed: https://chromium.googlesource.com/chromium/src/+/d0aa1e57ed2f964784b89b70c77a51b1bf833af1

[rkjnsn, 2017-03-22 22:31:30]

rkjnsn@chromium.org changed reviewers:
+ jamiewalch@chromium.org, sergeyu@chromium.org

[rkjnsn, 2017-03-22 22:31:31]

This is an alternative to https://codereview.chromium.org/2710023003/ which
provides the needed functionality much less invasively, and avoids the need to
emulate various PolicyWatcher behavior in a mock.

[Sergey Ulanov, 2017-03-23 01:11:43]

lgtm

[rkjnsn, 2017-03-29 22:14:34]

The CQ bit was checked by rkjnsn@chromium.org

[commit-bot: I haz the power, 2017-03-29 22:15:25]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-03-30 00:17:32]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1490825674847050, "parent_rev":
"43d841d52e2c28931f80ab41adf564e8d0912bb0", "commit_rev":
"d0aa1e57ed2f964784b89b70c77a51b1bf833af1"}

[commit-bot: I haz the power, 2017-03-30 00:18:52]

Description was changed from

==========
Support PolicyWatcher with custom loader for testing

PolicyWatcher::Create automatically creates an underlying
AsyncPolicyLoader corresponding to the policy storage location of the
current platform. This commit adds an alternative constructor,
CreateFromPolicyLoaderForTesting, which allows a custom
AsyncPolicyLoader to be specified to allow testing other components with
different policy configurations.
==========

to

==========
Support PolicyWatcher with custom loader for testing

PolicyWatcher::Create automatically creates an underlying
AsyncPolicyLoader corresponding to the policy storage location of the
current platform. This commit adds an alternative constructor,
CreateFromPolicyLoaderForTesting, which allows a custom
AsyncPolicyLoader to be specified to allow testing other components with
different policy configurations.

Review-Url: https://codereview.chromium.org/2764333003
Cr-Commit-Position: refs/heads/master@{#460592}
Committed:
https://chromium.googlesource.com/chromium/src/+/d0aa1e57ed2f964784b89b70c77a...
==========

[commit-bot: I haz the power, 2017-03-30 00:18:54]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/d0aa1e57ed2f964784b89b70c77a...