[vm, gc] Require a safepoint for heap iteration.

runtime/vm/become.cc

 // Copyright (c) 2016, 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/become.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 
 #include "vm/dart_api_state.h"
@@ skipping 197 matching lines @@
     OS::PrintErr("AFTER OBJECT AS STRING=%s\n", obj.ToCString());
   }
 }
 
 void Become::ElementsForwardIdentity(const Array& before, const Array& after) {
   Thread* thread = Thread::Current();
   Isolate* isolate = thread->isolate();
   Heap* heap = isolate->heap();
 
   TIMELINE_FUNCTION_GC_DURATION(thread, "Become::ElementsForwardIdentity");
-  HeapIterationScope his;
+  HeapIterationScope his(thread);
 
   // Setup forwarding pointers.
   ASSERT(before.Length() == after.Length());
   for (intptr_t i = 0; i < before.Length(); i++) {
     RawObject* before_obj = before.At(i);
     RawObject* after_obj = after.At(i);
 
     if (before_obj == after_obj) {
       FATAL("become: Cannot self-forward");
     }
@@ skipping 61 matching lines @@
   }
 
 #if defined(DEBUG)
   for (intptr_t i = 0; i < before.Length(); i++) {
     ASSERT(before.At(i) == after.At(i));
   }
 #endif
 }
 
 }  // namespace dart