Use symbols when looking up fields in a class

runtime/lib/math.cc

Index: runtime/lib/math.cc
diff --git a/runtime/lib/math.cc b/runtime/lib/math.cc
index 8e5e750cd1fc6440760fcb697391a55a71366b31..0199782bdfa6ecd0ca9f0f3a276c71bd784a77d6 100644
--- a/runtime/lib/math.cc
+++ b/runtime/lib/math.cc
@@ -79,7 +79,7 @@ DEFINE_NATIVE_ENTRY(Math_doublePow, 2) {
 static RawTypedData* GetRandomStateArray(const Instance& receiver) {
   const Class& random_class = Class::Handle(receiver.clazz());
   const Field& state_field =
-      Field::Handle(random_class.LookupField(Symbols::_state()));
+      Field::Handle(random_class.LookupFieldAllowPrivate(Symbols::_state()));
   ASSERT(!state_field.IsNull());
   const Instance& state_field_value =
       Instance::Cast(Object::Handle(receiver.GetField(state_field)));