Add an explicit ObjectWatcher::IsWatching() method

Add an explicit ObjectWatcher::IsWatching() method

This removes the need to compare a raw handle against
a predefined value from the caller's code.

BUG=none
TEST=base_unittests

Committed: https://crrev.com/51f3aacf25ac2246a2ea5e346a2e4962da2544d6
Cr-Commit-Position: refs/heads/master@{#314687}

[rvargas (doing something else), 2015-02-04 03:22:21]

rvargas@chromium.org changed reviewers:
+ cpu@chromium.org

[cpu_(ooo_6.6-7.5), 2015-02-05 00:31:44]

lgtm

[rvargas (doing something else), 2015-02-05 00:43:01]

The CQ bit was checked by rvargas@chromium.org

[commit-bot: I haz the power, 2015-02-05 00:44:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/868143004/1

[commit-bot: I haz the power, 2015-02-05 00:49:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-05 00:51:13]

Patchset 1 (id:??) landed as
https://crrev.com/51f3aacf25ac2246a2ea5e346a2e4962da2544d6
Cr-Commit-Position: refs/heads/master@{#314687}