Resolve a few errors with the new collector and the dalvik tests.

Resolve a few errors with the new collector and the dalvik tests.

* First, Scavenge class object instance fields.  This fixes a crash in
  the 067-preemptive-unpark test.

* Assert that allocations to back the transport of gray objects
  succeeds.  Fragmentation caused by pinning can cause a blow-up in
  the size of to-space.  Until we can perform emergency promotions
  this leads to more diagnosable test failures.

* Zero dvmHeapSweepUnmarkObjects's out parameters.  This silences some
  valgrind errors.

Change-Id: Iafbd915f2020418d584477b58c512b9ff4637213