Ignore deleted handles when processing weak roots.

runtime/vm/scavenger.cc

 // Copyright (c) 2011, 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.
 
 #include "vm/scavenger.h"
 
 #include "vm/dart.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 122 matching lines @@
 
 class ScavengerWeakVisitor : public HandleVisitor {
  public:
   explicit ScavengerWeakVisitor(Scavenger* scavenger) : scavenger_(scavenger) {
   }
 
   void VisitHandle(uword addr) {
     WeakPersistentHandle* handle =
         reinterpret_cast<WeakPersistentHandle*>(addr);
     RawObject* raw_obj = handle->raw();
+    if (!raw_obj->IsHeapObject()) {
+      // Deleted handles are identified by a Smi as the raw object value.
+      return;
+    }
     uword raw_addr = RawObject::ToAddr(raw_obj);
     if (scavenger_->from_->Contains(raw_addr)) {
       uword header = *reinterpret_cast<uword*>(raw_addr);
       if (IsForwarding(header)) {
         handle->set_raw(RawObject::FromAddr(ForwardedAddr(header)));
       } else {
         WeakPersistentHandle::Finalize(handle);
       }
     }
   }
@@ skipping 144 matching lines @@
     OS::PrintErr(" done.\n");
   }
 
   count_++;
   // Done scavenging. Reset the marker.
   ASSERT(scavenging_);
   scavenging_ = false;
 }
 
 }  // namespace dart