Debug garbage collector does not correctly remove cross-gen garbage

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 RUNTIME_VM_HEAP_H_
 #define RUNTIME_VM_HEAP_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/flags.h"
@@ skipping 227 matching lines @@
 
   Isolate* isolate() const { return isolate_; }
 
   Monitor* barrier() const { return barrier_; }
   Monitor* barrier_done() const { return barrier_done_; }
 
   void SetupImagePage(void* pointer, uword size, bool is_executable) {
     old_space_.SetupImagePage(pointer, size, is_executable);
   }
 
+  bool IsDebugCollection() { return debug_gc_in_progress_; }

[rmacnak, 2017/06/08 21:23:48]

Unused

+
  private:
   class GCStats : public ValueObject {
    public:
     GCStats() {}
     intptr_t num_;
     Heap::Space space_;
     Heap::GCReason reason_;
 
     class Data : public ValueObject {
      public:
@@ skipping 81 matching lines @@
   GCStats stats_;
 
   // This heap is in read-only mode: No allocation is allowed.
   bool read_only_;
 
   // GC on the heap is in progress.
   Monitor gc_in_progress_monitor_;
   bool gc_new_space_in_progress_;
   bool gc_old_space_in_progress_;
 
+  // Debug GC is in progress
+  bool debug_gc_in_progress_;
+
   friend class Become;       // VisitObjectPointers
   friend class Precompiler;  // VisitObjects
   friend class ObjectGraph;  // VisitObjects
   friend class Unmarker;     // VisitObjects
   friend class ServiceEvent;
   friend class PageSpace;             // VerifyGC
   friend class IsolateReloadContext;  // VisitObjects
   friend class ClassFinalizer;        // VisitObjects
 
   DISALLOW_COPY_AND_ASSIGN(Heap);
@@ skipping 28 matching lines @@
 // Note: During this scope, the code pages are non-executable.
 class WritableVMIsolateScope : StackResource {
  public:
   explicit WritableVMIsolateScope(Thread* thread);
   ~WritableVMIsolateScope();
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_HEAP_H_