Add logging system to pub and sprinkle some logging in.

utils/pub/command_update.dart

Index: utils/pub/command_update.dart
diff --git a/utils/pub/command_update.dart b/utils/pub/command_update.dart
index 16155e2bf9940e5d44bb0340953f1aa3fbc144ac..daedfb6a19d715ecda949c74d89b30140868713b 100644
--- a/utils/pub/command_update.dart
+++ b/utils/pub/command_update.dart
@@ -5,6 +5,7 @@
 library command_update;
 
 import 'entrypoint.dart';
+import 'log.dart' as log;
 import 'pub.dart';
 
 /** Handles the `update` pub command. */
@@ -21,6 +22,6 @@ class UpdateCommand extends PubCommand {
     } else {
       future = entrypoint.updateDependencies(commandOptions.rest);
     }
-    return future.transform((_) => print("Dependencies updated!"));
+    return future.transform((_) => log.message("Dependencies updated!"));
   }
 }