Fixed initialization bug.

It turns out that calling OSAtomicCompareAndSwap32Barrier with
unitialized memory is not a good idea. Changed to initialize
atomic values with assignment, which is fine since constructors
are not expected to be thread safe.

Change-Id: Ibdfc4ac761a2a238fb4794f9644aaf944b183447
Merge topic 'atomic-init-fix' into master

aef03fa2 Fixed initialization bug.