Fail gracefully when attempting to evaluate against a VM internal class such a Field.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 3070 matching lines @@
   func.SetNumOptionalParameters(0, true);
   func.SetIsOptimizable(false);
   return func.raw();
 }
 
 
 RawObject* Class::Evaluate(const String& expr,
                            const Array& param_names,
                            const Array& param_values) const {
   ASSERT(Thread::Current()->IsMutatorThread());
+  if (id() < kInstanceCid) {
+    const Instance& exception = Instance::Handle(String::New(
+        "Cannot evaluate against a VM internal class"));
+    const Instance& stacktrace = Instance::Handle();
+    return UnhandledException::New(exception, stacktrace);
+  }
+
   const Function& eval_func =
       Function::Handle(EvaluateHelper(*this, expr, param_names, true));
   const Object& result =
       Object::Handle(DartEntry::InvokeFunction(eval_func, param_values));
   return result.raw();
 }
 
 
 // Ensure that top level parsing of the class has been done.
 RawError* Class::EnsureIsFinalized(Thread* thread) const {
@@ skipping 19605 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart