Make the "sticky error" an Error instead of a String.

runtime/vm/object_store.cc

 // Copyright (c) 2011, 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_store.h"
 
 #include "vm/exceptions.h"
 #include "vm/isolate.h"
 #include "vm/longjump.h"
 #include "vm/object.h"
@@ skipping 31 matching lines @@
     false_value_(Bool::null()),
     empty_array_(Array::null()),
     symbol_table_(Array::null()),
     canonical_type_arguments_(Array::null()),
     core_library_(Library::null()),
     core_impl_library_(Library::null()),
     native_wrappers_library_(Library::null()),
     root_library_(Library::null()),
     registered_libraries_(Library::null()),
     pending_classes_(Array::null()),
-    sticky_error_(String::null()),
+    sticky_error_(Error::null()),
     empty_context_(Context::null()),
     stack_overflow_(Instance::null()),
     out_of_memory_(Instance::null()),
     preallocate_objects_called_(false) {
 }
 
 
 ObjectStore::~ObjectStore() {
 }
 
@@ skipping 146 matching lines @@
     return kBoolInterface;
   } else if (raw_type == string_interface()) {
     return kStringInterface;
   } else if (raw_type == list_interface()) {
     return kListInterface;
   }
   return kInvalidIndex;
 }
 
 }  // namespace dart