Change Duration to take proper named optional parameters.

runtime/lib/date_patch.dart

Index: runtime/lib/date_patch.dart
diff --git a/runtime/lib/date_patch.dart b/runtime/lib/date_patch.dart
index 914aab83ab665996d402587d057b9280d6a924e5..7898957ad17b1c893e9a4d584d5ea7821ce78015 100644
--- a/runtime/lib/date_patch.dart
+++ b/runtime/lib/date_patch.dart
@@ -31,7 +31,7 @@ patch class DateImplementation {
   }
 
   /* patch */ Duration get timeZoneOffset {
-    if (isUtc) return new Duration(0);
+    if (isUtc) return new Duration();

[Lasse Reichstein Nielsen, 2012/09/13 09:30:46]

If not introducing the zero-duration, be consistent and use milliseconds: 0
here.

[kasperl, 2012/09/13 09:45:50]

I'm reluctant to start refactoring these things while I'm still trying to get
through all the code and "upgrade" it to the new optional parameter syntax and
semantics.

This is just the first of a ton of changes to the core libraries that we need to
do to enable the new semantics of positional optional parameters.

     int offsetInSeconds = _timeZoneOffsetInSeconds(millisecondsSinceEpoch);
     return new Duration(seconds: offsetInSeconds);
   }