Add num.sign getter.

sdk/lib/core/double.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.
 
 part of dart.core;
 
 // TODO: Convert this abstract class into a concrete class double
 // that uses the patch class functionality to account for the
 // different platform implementations.
 
@@ skipping 42 matching lines @@
    */
   int operator ~/(num other);
 
   /** Negate operator. */
   double operator -();
 
   /** Returns the absolute value of this [double]. */
   double abs();
 
   /**
+   * Returns the sign of the double's numerical value.
+   *
+   * Returns -1.0 if the value is less than zero,
+   * +1.0 if the value is greater than zero,
+   * and the value itself if it is -0.0, 0.0 or NaN.
+   */
+  double get sign;
+
+  /**
    * Returns the integer closest to `this`.
    *
    * Rounds away from zero when there is no closest integer:
    *  [:(3.5).round() == 4:] and [:(-3.5).round() == -4:].
    *
    * If `this` is not finite (`NaN` or infinity), throws an [UnsupportedError].
    */
   int round();
 
   /**
@@ skipping 93 matching lines @@
    *     "0."
    *     ".0"
    *     "-1.e3"
    *     "1234E+7"
    *     "+.12e-9"
    *     "-NaN"
    */
   external static double parse(String source,
                                [double onError(String source)]);
 }