Fixes race condition in messagemeter.h (#3377)
Fixes race condition in messagemeter.h (#3377)

SDLCORE-373

Unprotected critical section accessed by two different threads,
timing_map was being modified by clearing the map identifiers causing a
crash in boost::date_time
Review: Change RWLock to Lock, Added FrequencyImpl private method

Co-authored-by: Mario Godinez <d281e7c28622232a952cc9359bf57c91d7d204cd@ford.com>
smartdevicelink/sdl_core,smartdevicelink/sdl_core,smartdevicelink/sdl_core,smartdevicelink/sdl_core