Pass in the isolate parameter to the weak persistent callback handler so that

runtime/vm/verifier.h

Index: runtime/vm/verifier.h
===================================================================
--- runtime/vm/verifier.h	(revision 33281)
+++ runtime/vm/verifier.h	(working copy)
@@ -54,7 +54,8 @@
 class VerifyWeakPointersVisitor : public HandleVisitor {
  public:
   explicit VerifyWeakPointersVisitor(VerifyPointersVisitor* visitor)
-      : visitor_(visitor) {
+      :  HandleVisitor(Isolate::Current()),
+         visitor_(visitor) {
   }
 
   virtual void VisitHandle(uword addr, bool is_prologue_weak);