Added nextIntRange to dartvm and dart2js.

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

Index: sdk/lib/_internal/compiler/implementation/lib/math_patch.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/math_patch.dart b/sdk/lib/_internal/compiler/implementation/lib/math_patch.dart
index b20276efa101c5aad9e728ab4130eaee1d78cc30..1c74daef012313176b7c73b364b541af978028db 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/math_patch.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/math_patch.dart
@@ -54,6 +54,15 @@ class _Random implements Random {
     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.