Fix incorrect assertion failures in noopt regarding removing classes that still have constants.

runtime/vm/heap.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_HEAP_H_
 #define VM_HEAP_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/flags.h"
@@ skipping 106 matching lines @@
   RawObject* FindNewObject(FindObjectVisitor* visitor) const;
   RawObject* FindObject(FindObjectVisitor* visitor) const;
 
   void CollectGarbage(Space space);
   void CollectGarbage(Space space, ApiCallbacks api_callbacks, GCReason reason);
   void CollectAllGarbage();
   bool NeedsGarbageCollection() const {
     return old_space_.NeedsGarbageCollection();
   }
 
+#if defined(DEBUG)
+  void WaitForSweeperTasks();
+#endif
+
   // Enables growth control on the page space heaps.  This should be
   // called before any user code is executed.
   void InitGrowthControl();
   void EnableGrowthControl() { SetGrowthControlState(true); }
   void DisableGrowthControl() { SetGrowthControlState(false); }
   void SetGrowthControlState(bool state);
   bool GrowthControlState();
 
   // Protect access to the heap. Note: Code pages are made
   // executable/non-executable when 'read_only' is true/false, respectively.
@@ skipping 253 matching lines @@
   explicit WritableVMIsolateScope(Thread* thread, bool include_code_pages);
   ~WritableVMIsolateScope();
 
  private:
   bool include_code_pages_;
 };
 
 }  // namespace dart
 
 #endif  // VM_HEAP_H_