Add OWNERS file for chrome/browser/resources/webstore_app

It's typically extensions/apps team members making changes to the manifest file
here.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/8789001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@112803 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/webstore_app/OWNERS

+# Extensions / Apps team members.
+aa@chromium.org
+asargent@chromium.org
+bolms@chromium.org
+erikkay@chromium.org
+finnur@chromium.org
+jstritar@chromium.org
+mihaip@chromium.org
+miket@chromium.org
+mpcomplete@chromium.org
+yoz@chromium.org