Add comparison operators to Date class.

corelib/src/date.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.
 
 // Dart core library.
 
 /**
  * Date is the public interface to a point in time.
  */
 interface Date extends Comparable, Hashable default DateImplementation {
@@ skipping 65 matching lines @@
    *
    * This constructor is the only one that doesn't need to be computations and
    * which can therefore be [:const:].
    *
    * The constructed [Date] represents 1970-01-01T00:00:00Z + [value]ms in
    * the given [timeZone].
    */
   const Date.fromEpoch(int value, TimeZone timeZone);
 
   /**
+   * Returns true if [this] occurs before [other]. The comparison is independent
+   * of the timezone the [Date] is in.
+   */
+  bool operator <(Date other);
+  /**
+   * Returns true if [this] occurs at the same time or before [other]. The
+   * comparison is independent of the timezone the [Date] is in.
+   */
+  bool operator <=(Date other);
+  /**
+   * Returns true if [this] occurs after [other]. The comparison is independent
+   * of the timezone the [Date] is in.
+   */
+  bool operator >(Date other);
+  /**
+   * Returns true if [this] occurs at the same time or after [other]. The
+   * comparison is independent of the timezone the [Date] is in.
+   */
+  bool operator >=(Date other);
+
+  /**
    * Returns a new [Date] in the given [targetTimeZone] time zone. The
    * [value] of the new instance is equal to [:this.value:].
    *
    * This call is equivalent to
    *  [:new Date.fromEpoch(this.value, targetTimeZone):].
    */
   Date changeTimeZone(TimeZone targetTimeZone);
 
   /**
    * Returns the year.
@@ skipping 72 matching lines @@
   /**
    * Returns a new [Date] with the [duration] subtracted from this instance.
    */
   Date subtract(Duration duration);
 
   /**
    * Returns a [Duration] with the difference of [:this:] and [other].
    */
   Duration difference(Date other);
 }