VM: Precompile method extractors for implicit and explicit closurization.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 2c94f2dcbe7a6df8dfca59c49184a74f6a5a97aa..98c821fe2b2e258540c81ea36371223a5cb12e64 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2570,6 +2570,9 @@ class Function : public Object {
                                       const Script& script,
                                       bool is_static);
 
+  RawFunction* CreateMethodExtractor(const String& getter_name) const;
+  RawFunction* GetMethodExtractor(const String& getter_name) const;
+
   // Allocate new function object, clone values from this function. The
   // owner of the clone is new_owner.
   RawFunction* Clone(const Class& new_owner) const;