Make it easier to run an optimized build, turn the GC timings back on, and remove some unnecessary code.

The Class* field is a regular instance field now, so no need to scan it twice.
We do our null checking in ScanObject, so we don't need to duplicate the checks
in each child.

Also count the number of class, array, and other objects we scan.

Change-Id: I9034708d5e0e1edffaccf3cad4785c5fccf3b38e
diff --git a/src/heap.h b/src/heap.h
index 829bbb2..932d490 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -52,7 +52,7 @@
   static void Destroy();
 
   static bool IsVerboseHeap() {
-    return is_verbose_heap_;
+    return is_verbose_heap_ || is_verbose_gc_ /* TODO: remove when pause times are down */;
   }
 
   static bool IsVerboseGc() {