Add a 'secure' constructor to Random in dart:math returning a cryptographically

tests/lib/math/random_test.dart

Index: tests/lib/math/random_test.dart
diff --git a/tests/lib/math/random_test.dart b/tests/lib/math/random_test.dart
index f769efb793e691f69c13232324e0ad58d3b55ab2..d969e4b5e0ad33b313f1063f93b99a2589cffde1 100644
--- a/tests/lib/math/random_test.dart
+++ b/tests/lib/math/random_test.dart
@@ -56,6 +56,7 @@ void checkSequence() {
   Expect.equals( 226275094, rnd.nextInt(i *= 2));
   Expect.equals(1639629168, rnd.nextInt(i *= 2));
   Expect.equals(0x100000000, i);
+  Expect.equals( 1552504971, rnd.nextInt(i));

[Lasse Reichstein Nielsen, 2015/10/15 09:32:33]

Why? We already called with that value of max above.

[regis, 2015/10/15 17:12:02]

Aargh. Left over from debugging. Reverted.

I was trying to figure out why is this test not failing, since we have the wrong
check in nextInt:
(rnd32 - result + max) >= _POW2_32
instead of
(rnd32 - result + max) > _POW2_32

The reason it succeeds is that we use another code path if max is a power of 2.

   // If max is too large expect an ArgumentError.
   Expect.throws(() => rnd.nextInt(i + 1), (e) => e is ArgumentError);