Reapply "Improve hashCode for closure objects" with fixes.

runtime/vm/dart_entry.cc

Index: runtime/vm/dart_entry.cc
diff --git a/runtime/vm/dart_entry.cc b/runtime/vm/dart_entry.cc
index a59b9dff76940c458f3832f52b429d646d822a59..fd91fb0b017106352f93bfeae2ebfe54131cb076 100644
--- a/runtime/vm/dart_entry.cc
+++ b/runtime/vm/dart_entry.cc
@@ -509,6 +509,24 @@ RawObject* DartLibraryCalls::Equals(const Instance& left,
   return result.raw();
 }
 
+// On success, returns a RawInstance.  On failure, a RawError.
+RawObject* DartLibraryCalls::IdentityHashCode(const Instance& object) {
+  const int kNumArguments = 1;
+  Thread* thread = Thread::Current();
+  Zone* zone = thread->zone();
+  const Library& libcore = Library::Handle(zone, Library::CoreLibrary());
+  ASSERT(!libcore.IsNull());
+  const Function& function = Function::Handle(
+      zone, libcore.LookupFunctionAllowPrivate(Symbols::identityHashCode()));
+  ASSERT(!function.IsNull());
+  const Array& args = Array::Handle(zone, Array::New(kNumArguments));
+  args.SetAt(0, object);
+  const Object& result =
+      Object::Handle(zone, DartEntry::InvokeFunction(function, args));
+  ASSERT(result.IsInstance() || result.IsError());
+  return result.raw();
+}
+
 RawObject* DartLibraryCalls::LookupHandler(Dart_Port port_id) {
   Thread* thread = Thread::Current();
   Zone* zone = thread->zone();