1. Provide a framework to traverse persistent prolog weak handles.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 34879)
+++ runtime/vm/object.cc	(working copy)
@@ -12621,6 +12621,17 @@
 }
 
 
+intptr_t* Instance::NativeFieldsDataAddr() const {
+  NoGCScope no_gc;
+  RawTypedData* native_fields =
+      reinterpret_cast<RawTypedData*>(*NativeFieldsAddr());
+  if (native_fields == TypedData::null()) {
+    return NULL;
+  }
+  return reinterpret_cast<intptr_t*>(native_fields->ptr()->data_);
+}
+
+
 void Instance::SetNativeField(int index, intptr_t value) const {
   ASSERT(IsValidNativeIndex(index));
   Object& native_fields = Object::Handle(*NativeFieldsAddr());