Make the implementations of InstanceMirror.hashCode use dart:core's identityHashCode.

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index 754aa5f82df967574e1898f8cbb33abd062fc827..f6cb3104fc53c44d0e5eba3664ef3084adb092de 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -1064,18 +1064,6 @@ DEFINE_NATIVE_ENTRY(TypeVariableMirror_upper_bound, 1) {
 }
 
 
-DEFINE_NATIVE_ENTRY(InstanceMirror_identityHash, 1) {
-  GET_NATIVE_ARGUMENT(Instance, reflectee, arguments->NativeArgAt(0));
-  ObjectStore* object_store = isolate->object_store();
-  const Class& cls = Class::Handle(isolate, object_store->object_class());
-  const Function& function =
-      Function::Handle(isolate, cls.LookupDynamicFunction(Symbols::hashCode()));
-  const Array& args = Array::Handle(isolate, Array::New(1));
-  args.SetAt(0, reflectee);
-  return DartEntry::InvokeFunction(function, args);
-}
-
-
 DEFINE_NATIVE_ENTRY(InstanceMirror_invoke, 5) {
   // Argument 0 is the mirror, which is unused by the native. It exists
   // because this native is an instance method in order to be polymorphic