- Revert parts of r39731 as they cause conflicting results.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
===================================================================
--- runtime/vm/raw_object.h	(revision 39731)
+++ runtime/vm/raw_object.h	(working copy)
@@ -330,13 +330,7 @@
   void ClearMarkBit() {
     ASSERT(IsMarked());
     uword tags = ptr()->tags_;
-    uword old_tags;
-    do {
-      old_tags = tags;
-      uword new_tags = MarkBit::update(false, old_tags);
-      tags = AtomicOperations::CompareAndSwapWord(
-          &ptr()->tags_, old_tags, new_tags);
-    } while (tags != old_tags);
+    ptr()->tags_ = MarkBit::update(false, tags);
   }
 
   // Support for GC watched bit.
@@ -389,23 +383,11 @@
   void SetRememberedBit() {
     ASSERT(!IsRemembered());
     uword tags = ptr()->tags_;
-    uword old_tags;
-    do {
-      old_tags = tags;
-      uword new_tags = RememberedBit::update(true, old_tags);
-      tags = AtomicOperations::CompareAndSwapWord(
-          &ptr()->tags_, old_tags, new_tags);
-    } while (tags != old_tags);
+    ptr()->tags_ = RememberedBit::update(true, tags);
   }
   void ClearRememberedBit() {
     uword tags = ptr()->tags_;
-    uword old_tags;
-    do {
-      old_tags = tags;
-      uword new_tags = RememberedBit::update(false, old_tags);
-      tags = AtomicOperations::CompareAndSwapWord(
-          &ptr()->tags_, old_tags, new_tags);
-    } while (tags != old_tags);
+    ptr()->tags_ = RememberedBit::update(false, tags);
   }
 
   bool IsDartInstance() {