Report compile-time errors for conflicting overrides as specified by latest

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 26300)
+++ runtime/vm/parser.cc	(working copy)
@@ -3122,7 +3122,7 @@
   }
   if (members->FieldNameExists(*field->name, !field->has_final)) {
     ErrorMsg(field->name_pos,
-             "'%s' field/method already defined\n", field->name->ToCString());
+             "field or method '%s' already defined", field->name->ToCString());
   }
   Function& getter = Function::Handle();
   Function& setter = Function::Handle();