Add barriers for proper observation sequence.

Change-Id: I5c2ef043920fe60c92304cd2c8a857a805b6e9af
GC triggering performance optimizations

Copy the correct starting heap size at process init.
Interfaces to set GC/managed heap parameters.

Change-Id: I454b1985a3225d7dbdea9c5d4e6f0c9f5e24352e