Cache hash code for closures.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 816a79889cb1d0e1b5987e97cadfc7783369d37a..2c62d62d738e1cc0dc7a0e43913d3c49c5be17fd 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2347,6 +2347,8 @@ class Function : public Object {
 
   RawInstance* ImplicitInstanceClosure(const Instance& receiver) const;
 
+  RawSmi* GetClosureHashCode() const;
+
   // Redirection information for a redirecting factory.
   bool IsRedirectingFactory() const;
   RawType* RedirectionType() const;
@@ -3015,6 +3017,9 @@ class ClosureData : public Object {
   RawInstance* implicit_static_closure() const { return raw_ptr()->closure_; }
   void set_implicit_static_closure(const Instance& closure) const;
 
+  RawObject* hash() const { return raw_ptr()->hash_; }
+  void set_hash(intptr_t value) const;
+
   static RawClosureData* New();
 
   FINAL_HEAP_OBJECT_IMPLEMENTATION(ClosureData, Object);