[Telemetry] Have android choose the best available source of power monitoring.

This CL adds the monsoon power monitor for telemetry power measurement.
It also updates the android implementation to choose the best power
monitoring source available.

R=jeremy@chromium.org,tonyg@chromium.org

Review URL: https://codereview.chromium.org/159803002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250709 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250709