Parse annotations within LogEvent

This is a preliminary CL that parses annotations within LogEvent, but
does nothing with the annotations provided. Annotation information will
be exposed from LogEvent/FieldValue in a future CL. (That CL will also
contain tests for parsing annotations.)

Test: m statsd
Bug: 150414043
Change-Id: Iae79644ea8455280a654076bfd5819927d4183d3
2 files changed