Debug garbage collector does not correctly remove cross-gen garbage

runtime/vm/scavenger.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 RUNTIME_VM_SCAVENGER_H_
 #define RUNTIME_VM_SCAVENGER_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/dart.h"
@@ skipping 129 matching lines @@
     top_ += size;
     ASSERT(to_->Contains(top_) || (top_ == to_->end()));
     return result;
   }
 
   // Collect the garbage in this scavenger.
   void Scavenge();
   void Scavenge(bool invoke_api_callbacks);
 
   // Promote all live objects.
-  void Evacuate() {
-    Scavenge();
-    Scavenge();
-    ASSERT(UsedInWords() == 0);
-  }
+  void Evacuate();
 
   // Accessors to generate code for inlined allocation.
   uword* TopAddress() { return &top_; }
   uword* EndAddress() { return &end_; }
   static intptr_t top_offset() { return OFFSET_OF(Scavenger, top_); }
   static intptr_t end_offset() { return OFFSET_OF(Scavenger, end_); }
 
   int64_t UsedInWords() const {
     return (top_ - FirstObjectStart()) >> kWordSizeLog2;
   }
@@ skipping 123 matching lines @@
   RawWeakProperty* delayed_weak_properties_;
 
   int64_t gc_time_micros_;
   intptr_t collections_;
   static const int kStatsHistoryCapacity = 2;
   RingBuffer<ScavengeStats, kStatsHistoryCapacity> stats_history_;
 
   // The total size of external data associated with objects in this scavenger.
   intptr_t external_size_;
 
+  bool failed_to_promote_;
+
   friend class ScavengerVisitor;
   friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_SCAVENGER_H_