Fix type check to perform a subtype test at top level instead of an

runtime/vm/exceptions.cc

Index: runtime/vm/exceptions.cc
===================================================================
--- runtime/vm/exceptions.cc	(revision 5412)
+++ runtime/vm/exceptions.cc	(working copy)
@@ -223,12 +223,12 @@
     OS::Print("'%s': Failed type check: line %d pos %d: ",
               String::Handle(script.url()).ToCString(), line, column);
     if (!dst_name.IsNull() && (dst_name.Length() > 0)) {
-      OS::Print("type '%s' is not assignable to type '%s' of '%s'.\n",
+      OS::Print("type '%s' is not a subtype of type '%s' of '%s'.\n",
                 src_type_name.ToCString(),
                 dst_type_name.ToCString(),
                 dst_name.ToCString());
     } else {
-      OS::Print("malformed type used in type test.\n",
+      OS::Print("malformed type used.\n",
                 String::Handle(script.url()).ToCString(),
                 line, column);
     }