Added nextIntRange to dartvm and dart2js.

sdk/lib/_internal/compiler/implementation/lib/math_patch.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.
 
 // Patch file for dart:math library.
 
 patch double sqrt(num x)
   => JS('double', r'Math.sqrt(#)', checkNum(x));
 
 patch double sin(num x)
@@ skipping 36 matching lines @@
 class _Random implements Random {
   // The Dart2JS implementation of Random doesn't use a seed.
   const _Random();
 
   int nextInt(int max) {
     if (max < 0) throw new ArgumentError("negative max: $max");
     if (max > 0xFFFFFFFF) max = 0xFFFFFFFF;
     return JS("int", "(Math.random() * #) >>> 0", max);
   }
 
+  int nextIntRange(int min, int max) {
+    if (max < 0) throw new ArgumentError("negative max: $max");
+    if (min >= max) throw new ArgumentError("min is greater then or equal to max");

[floitsch, 2013/11/18 13:36:03]

80 chars. And the error message should contain the values.

+    
+    int range = max - min;
+    range = nextInt(range);

[floitsch, 2013/11/18 13:36:03]

Don't reuse the variable (which is not a range).
I would just write it in one line:
return min + nextInt(max - min);

+    return min + range;
+  }
+
   /**
    * Generates a positive random floating point value uniformly distributed on
    * the range from 0.0, inclusive, to 1.0, exclusive.
    */
   double nextDouble() => JS("double", "Math.random()");
 
   /**
    * Generates a random boolean value.
    */
   bool nextBool() => JS("bool", "Math.random() < 0.5");
 }