Add BUILD.gn file for components's startup_metric_utils target.

BUG=None
TEST=gn, ninja -C out/Default onc_component
R=brettw@chromium.org

Review URL: https://codereview.chromium.org/101423005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241262 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241262