Support StatsD sending broadcasts.

StatsD will send a broadcast when we're 90% of the way to our
allocated memory limit for the configuration. If the memory usage
goes over the limit, we just lose all the data for this config.

Also modifies the adb shell commands to facilitate debugging of the
broadcasts.

Test: Manually tested on marlin-eng with custom gmscore code.

Change-Id: I517a15bd4c959aa221802f84a51f13141a725102