Fix a memory leak in LogEvent

My previous understanding of the liblog api was wrong. Luckily it
is caught in time. Also added a memory profiling tool in another CL.

Test: statsd_test
      adb shell dumpsys meminfo
      adb shell cmd stats meminfo

Change-Id: I742af2a38e52e35edf0d4c77ccc35ede7019a73b