Unwrap AsyncErrors to find real error.

utils/pub/hosted_source.dart

Index: utils/pub/hosted_source.dart
diff --git a/utils/pub/hosted_source.dart b/utils/pub/hosted_source.dart
index 43922a21aae3287698e9f5f1fbe9737159b927a7..70b1440d297f093da1e20b8aad333f857786939e 100644
--- a/utils/pub/hosted_source.dart
+++ b/utils/pub/hosted_source.dart
@@ -119,6 +119,8 @@ class HostedSource extends Source {
   /// this tries to translate into a more user friendly error message. Always
   /// throws an error, either the original one or a better one.
   void _throwFriendlyError(ex, package, url) {
+    ex = getRealError(ex);
+
     if (ex is PubHttpException && ex.response.statusCode == 404) {
       throw 'Could not find package "$package" at $url.';
     }