Summary: During the work for 6829187 we have fixed a number of basic bugs which are logically grouped with 6815692 and 6858164 but which must be reviewed and pushed separately.
Reviewed-by: kvn, never

Summary: First mercurial integration of the code for the Garbage-First garbage collector.
Reviewed-by: apetrusenko, iveresov, jmasa, sgoldman, tonyp, ysr