Implement least upper bound.

sdk/lib/_internal/compiler/implementation/warnings.dart

 // 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.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 519 matching lines @@
       "Error: Constant expressions can't refer to type variables.",
       howToFix: "Try removing the type variable or replacing it with a "
                 "concrete type.",
       examples: const ["""
 class C<T> {
   const C();
 
   m(T t) => const C<T>();
 }
 
-void main() => new C().m(null);  
+void main() => new C().m(null);
 """
 ]);
 
 
   static const MessageKind INVALID_TYPE_VARIABLE_BOUND = const MessageKind(
       "Warning: '#{typeArgument}' is not a subtype of bound '#{bound}' for "
       "type variable '#{typeVariable}' of type '#{thisType}'.",
       howToFix: "Try to change or remove the type argument.",
       examples: const ["""
 class C<T extends num> {}
@@ skipping 1017 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }