Fix VM crash when ClosureMirror.findInContext operates on a fake function.

runtime/lib/mirrors.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 "lib/invocation_mirror.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/exceptions.h"
@@ skipping 1432 matching lines @@
   }
   return result.raw();
 }
 
 
 DEFINE_NATIVE_ENTRY(ClosureMirror_find_in_context, 2) {
   GET_NON_NULL_NATIVE_ARGUMENT(Instance, closure, arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(Array, lookup_parts, arguments->NativeArgAt(1));
   ASSERT(lookup_parts.Length() >= 1 && lookup_parts.Length() <= 3);
 
+  if (!closure.IsClosure()) {
+    const Array& result_tuple = Array::Handle(Array::New(2));
+    result_tuple.SetAt(0, Bool::False());
+    return result_tuple.raw();
+  }
+
   Function& function = Function::Handle();
   const bool callable = closure.IsCallable(&function, NULL);
   ASSERT(callable);
 
   const int parts_len = lookup_parts.Length();
   // Lookup name is always the last part.
   const String& lookup_name = String::Handle(String::RawCast(
       lookup_parts.At(parts_len - 1)));
 
   String& part_name = String::Handle();
@@ skipping 503 matching lines @@
 }
 
 
 DEFINE_NATIVE_ENTRY(VariableMirror_type, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Field& field = Field::Handle(ref.GetFieldReferent());
   return field.type();
 }
 
 }  // namespace dart