Pass in "mode" to transformer plugins.

sdk/lib/_internal/pub/lib/src/barback.dart

Index: sdk/lib/_internal/pub/lib/src/barback.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback.dart b/sdk/lib/_internal/pub/lib/src/barback.dart
index 84a069a3f28086e285a145dbb5a8691f8437c6fe..af154a4ee6f4130142aa46e1ec4e330a557e1d0a 100644
--- a/sdk/lib/_internal/pub/lib/src/barback.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback.dart
@@ -108,7 +108,8 @@ class TransformerId {
 /// monitor the app and its dependencies for any updates. Otherwise the state of
 /// the app when the server is started will be maintained.
 Future<BarbackServer> createServer(String host, int port, PackageGraph graph,
-    {Iterable<Transformer> builtInTransformers, bool watchForUpdates: true}) {
+    BarbackMode mode, {Iterable<Transformer> builtInTransformers,
+    bool watchForUpdates: true}) {
   var provider = new PubPackageProvider(graph);
   var barback = new Barback(provider);
 
@@ -140,7 +141,7 @@ Future<BarbackServer> createServer(String host, int port, PackageGraph graph,
         })
       ];
 
-      loadAllTransformers(server, graph, builtInTransformers).then((_) {
+      loadAllTransformers(server, graph, mode, builtInTransformers).then((_) {
         if (!completer.isCompleted) completer.complete(server);
       }).catchError((error, stackTrace) {
         if (!completer.isCompleted) completer.completeError(error, stackTrace);