Fix mojo dart:io IPv6 address printing

mojo/dart/embedder/io/mojo_patch.dart

Index: mojo/dart/embedder/io/mojo_patch.dart
diff --git a/mojo/dart/embedder/io/mojo_patch.dart b/mojo/dart/embedder/io/mojo_patch.dart
index c31c5fb23cf555aa36e565fc29a45687c1a672ec..d49c6c4a68501f74026eca76f3f3e31b155693b5 100644
--- a/mojo/dart/embedder/io/mojo_patch.dart
+++ b/mojo/dart/embedder/io/mojo_patch.dart
@@ -91,9 +91,14 @@ class _NetworkServiceCodec {
         r += '${digit}${divider}';
       }
     } else {
-      for (var i = 0; i < 16; i++) {
-        var digit = address[i].toRadixString(16);
-        var divider = (i != 15) ? ':' : '';
+      for (var i = 0; i < 16; i += 2) {
+        var first = '';

[vtl, 2015/08/24 21:39:12]

drive-by: I'm not sure why something like

var digit = (address[i] * 256 + address[i+1]).toRadixString(16);

wouldn't have been preferable. (This has the benefit of producing "0" for 0
instead of "00", etc.)

+        if (address[i] != 0) {
+          first = address[i].toRadixString(16).padLeft(2, '0');
+        }
+        var second = address[i + 1].toRadixString(16).padLeft(2, '0');
+        var digit = '$first$second';
+        var divider = (i != 14) ? ':' : '';
         r += '${digit}${divider}';
       }
     }