Renumber UMA constants.

Clearcut does not like negative or zero values for its histograms.

Also, consolidate all metrics constants in the Metrics.java file. In
cases where values are being obtained from elsewhere (e.g. State.action
constants), map those constants to constants defined in Metrics.java.
This will reduce occurrences of constants changes accidentally screwing
up metrics data.

BUG=26737132

Change-Id: Ia9fb88a49c3102afc2464d20653e2ee21cfc591f