Add more tests and argument check to Process.sleep

R=ager@google.com

Review URL: https://codereview.chromium.org//13497008

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@21054 260f80e4-7a28-3924-810f-c04153c831b5

sdk/lib/io/process.dart

@@ -46,7 +46,11 @@ set exitCode(int status) {
  * in a isolate while it is blocked in a [sleep] call.
  */
 void sleep(Duration duration) {
-  _ProcessUtils._sleep(duration.inMilliseconds);
+  int milliseconds = duration.inMilliseconds;
+  if (milliseconds < 0) {
+    throw new ArgumentError("sleep: duration cannot be negative");
+  }
+  _ProcessUtils._sleep(milliseconds);
 }
 
 /**

tests/standalone/io/sleep_test.dart

@@ -13,7 +13,10 @@ test(int milliseconds) {
 }
 
 main() {
+  test(0);
   test(1);
   test(10);
   test(100);
+  Expect.throws(() => sleep(new Duration(milliseconds: -1)),
+                (e) => e is ArgumentError);
 }