Enable card cleaning

Cards which do not map to image spaces are now cleared at the start of GC. Cards which map to image spaces are now processed when we go through all the dirty cards after recursive mark. Dirty cards are handled based on if they are either image space cards or cards invalidated by mutators during CMS.

Change-Id: I6c2dc177ebd3f7dc7bbbbd19ae67221371851ebe
diff --git a/src/heap.h b/src/heap.h
index d368158..de3caa2 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -233,7 +233,7 @@
   void RecordAllocationLocked(AllocSpace* space, const Object* object);
   void RecordImageAllocations(Space* space);
 
-  void CollectGarbageInternal(bool clear_soft_references);
+  void CollectGarbageInternal(bool concurrent, bool clear_soft_references);
 
   // Given the current contents of the alloc space, increase the allowed heap footprint to match
   // the target utilization ratio.  This should only be called immediately after a full garbage