Add num.sign getter.

sdk/lib/_internal/lib/js_number.dart

Index: sdk/lib/_internal/lib/js_number.dart
diff --git a/sdk/lib/_internal/lib/js_number.dart b/sdk/lib/_internal/lib/js_number.dart
index b6606f0699d05bc69b78691e46792946ac2ba618..7aaeb9369e78d33e73bd942db52a1188101ddcff 100644
--- a/sdk/lib/_internal/lib/js_number.dart
+++ b/sdk/lib/_internal/lib/js_number.dart
@@ -59,6 +59,8 @@ class JSNumber extends Interceptor implements num {
 
   num abs() => JS('num', r'Math.abs(#)', this);
 
+  num get sign => this > 0 ? 1 : this < 0 ? -1 : this;

[Søren Gjesse, 2013/12/13 11:45:04]

EcmaScript 6 has Math.sign with the same semantics
(https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Obje...),
but I guess we don't want to check whether that exists.

[Lasse Reichstein Nielsen, 2013/12/13 12:08:48]

Interesting. Did not know that.
Since it most likely doesn't exist yet, I don't think we'd want to use that any
time soon. When ES6 gets closer to finished, and implementations become ready,
we might want to look at it again.

We definitely don't want to test for existence every time, so it would be
something to do during startup.

+
   static const int _MIN_INT32 = -0x80000000;
   static const int _MAX_INT32 = 0x7FFFFFFF;
 
@@ -240,7 +242,7 @@ class JSNumber extends Interceptor implements num {
   }
 
   num operator >>(num other) {
-    if (false) _shrReceiverPositive(other); 
+    if (false) _shrReceiverPositive(other);

[sra1, 2014/03/07 00:53:35]

What is the purpose of this dead code?
Please delete it or explain it.

     if (other is !num) throw new ArgumentError(other);
     if (JS('num', '#', other) < 0) throw new ArgumentError(other);
     return _shrOtherPositive(other);