Add comparison operators to Date class.

lib/compiler/implementation/lib/mockimpl.dart

 // 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.
 
 // Mocks of classes and interfaces that Leg cannot read directly.
 
 // TODO(ahe): Remove this file.
 
 class JSSyntaxRegExp implements RegExp {
   final String pattern;
@@ skipping 260 matching lines @@
     }
   }
 
   const DateImplementation.fromEpoch(this.value, this.timeZone);
 
   bool operator ==(other) {
     if (!(other is DateImplementation)) return false;
     return (value == other.value) && (timeZone == other.timeZone);
   }
 
-  int compareTo(Date other) {
-    checkNull(other);
-    return value.compareTo(other.value);
-  }
+  bool operator <(Date other) => value < other.value;
+
+  bool operator <=(Date other) => value <= other.value;
+
+  bool operator >(Date other) => value > other.value;
+
+  bool operator >=(Date other) => value >= other.value;
+
+  int compareTo(Date other) => value.compareTo(other.value);
 
   int hashCode() => value;
 
   Date changeTimeZone(TimeZone targetTimeZone) {
     if (targetTimeZone == null) {
       targetTimeZone = new TimeZoneImplementation.local();
     }
     return new Date.fromEpoch(value, targetTimeZone);
   }
 
@@ skipping 90 matching lines @@
   factory List.from(Iterable<E> other) {
     List<E> result = new List<E>();
     // TODO(ahe): Use for-in when it is implemented correctly.
     Iterator<E> iterator = other.iterator();
     while (iterator.hasNext()) {
       result.add(iterator.next());
     }
     return result;
   }
 }