Fix bug in Duration.toString.

sdk/lib/core/duration.dart

Index: sdk/lib/core/duration.dart
diff --git a/sdk/lib/core/duration.dart b/sdk/lib/core/duration.dart
index 77633a67870abb60aee91d9a5e75f316555bc21e..d174012baa5bfd869c2a227d51c7c83e563c0c1b 100644
--- a/sdk/lib/core/duration.dart
+++ b/sdk/lib/core/duration.dart
@@ -23,7 +23,7 @@ part of dart.core;
  * Use one of the properties, such as [inDays],
  * to retrieve the integer value of the Duration in the specified time unit.
  * Note that the returned value is rounded down.
- * For example, 
+ * For example,
  *
  *     Duration aLongWeekend = new Duration(hours:88);
  *     assert(aLongWeekend.inDays == 3);
@@ -223,7 +223,7 @@ class Duration implements Comparable<Duration> {
       if (n >= 10000) return "0$n";
       if (n >= 1000) return "00$n";
       if (n >= 100) return "000$n";
-      if (n > 10) return "0000$n";
+      if (n >= 10) return "0000$n";
       return "00000$n";
     }
     String twoDigits(int n) {