Add histograms for DHCP lease expiry

Add per-network-technology histograms that will be emitted by
shill whenever a lease expires before it can be renewed.

R=isherman@chromium.org
BUG=216710
TEST=Start chrome, and browse to chrome://histograms to make sure
these enums now exist.

Review URL: https://codereview.chromium.org/124193002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243772 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243772