Add nick@chromium.org as OWNER for chrome/browser/task_manager

Add nick@chromium.org as OWNER for chrome/browser/task_manager

As of https://codereview.chromium.org/196693002 there is
no per-directory owner here, and I'm volunteering to take
reviews for this code. (Interestingly, I can't land
https://codereview.chromium.org/196623003/ because the
approving OWNER removed himself in the time period
between LGTM and the CQ).

My recent work with the following landed cls has given me
sufficient familiarity with this code:
https://codereview.chromium.org/185873003
https://codereview.chromium.org/191623003
https://codereview.chromium.org/186153002

Additionally, in the near future I plan to significantly
alter five of the resource providers (work-in-progress here
https://codereview.chromium.org/195163005/ ) and being OWNER
myself should make it easier break that big change up for
detailed, incremental review.

BUG=348836
TEST=None

Review URL: https://codereview.chromium.org/195813022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@258222 0039d316-1c4b-4281-b951-d872f2087c98