Use a tag bit for indicating prologue weak persistent handles, this avoids

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
===================================================================
--- runtime/vm/isolate.cc	(revision 33249)
+++ runtime/vm/isolate.cc	(working copy)
@@ -728,10 +728,10 @@
   FinalizeWeakPersistentHandlesVisitor() {
   }
 
-  void VisitHandle(uword addr) {
+  void VisitHandle(uword addr, bool is_prologue_weak) {
     FinalizablePersistentHandle* handle =
         reinterpret_cast<FinalizablePersistentHandle*>(addr);
-    FinalizablePersistentHandle::Finalize(handle);
+    FinalizablePersistentHandle::Finalize(handle, is_prologue_weak);
   }
 
  private:
@@ -779,8 +779,9 @@
 
     // Finalize any weak persistent handles with a non-null referent.
     FinalizeWeakPersistentHandlesVisitor visitor;
-    api_state()->weak_persistent_handles().VisitHandles(&visitor);
-    api_state()->prologue_weak_persistent_handles().VisitHandles(&visitor);
+    api_state()->weak_persistent_handles().VisitHandles(&visitor, false);
+    api_state()->prologue_weak_persistent_handles().VisitHandles(
+        &visitor, true);
 
     CompilerStats::Print();
     if (FLAG_trace_isolates) {