Cache hash code for closures.

runtime/lib/function.cc

Index: runtime/lib/function.cc
diff --git a/runtime/lib/function.cc b/runtime/lib/function.cc
index 2abdde715b7bd39bad4c78dcfd2ade0fe193a418..5b2343ff8ff8aa12c93d559535554ddbf6be1931 100644
--- a/runtime/lib/function.cc
+++ b/runtime/lib/function.cc
@@ -69,17 +69,7 @@ DEFINE_NATIVE_ENTRY(Closure_hashCode, 1) {
   const Closure& receiver =
       Closure::CheckedHandle(zone, arguments->NativeArgAt(0));
   const Function& func = Function::Handle(receiver.function());
-  // Hash together name, class name and signature.
-  const Class& cls = Class::Handle(func.Owner());
-  intptr_t result = String::Handle(func.name()).Hash();
-  result += String::Handle(func.Signature()).Hash();
-  result += String::Handle(cls.Name()).Hash();
-  // Finalize hash value like for strings so that it fits into a smi.
-  result += result << 3;
-  result ^= result >> 11;
-  result += result << 15;
-  result &= ((static_cast<intptr_t>(1) << String::kHashBits) - 1);
-  return Smi::New(result);
+  return func.GetClosureHashCode();
 }