Run pub tests against older versions of barback.

third_party/pkg/barback-0.13.0/test/transformer/log.dart

Index: third_party/pkg/barback-0.13.0/test/transformer/log.dart
diff --git a/pkg/barback/test/transformer/log.dart b/third_party/pkg/barback-0.13.0/test/transformer/log.dart
similarity index 57%
copy from pkg/barback/test/transformer/log.dart
copy to third_party/pkg/barback-0.13.0/test/transformer/log.dart
index 4e3dd72d5424428a19fc083dc10fb6305131a934..7866722c044afbc6319a2d585a2b1a1309cf37db 100644
--- a/pkg/barback/test/transformer/log.dart
+++ b/third_party/pkg/barback-0.13.0/test/transformer/log.dart
@@ -22,20 +22,22 @@ class LogTransformer extends MockTransformer {
 
   LogTransformer(this._entries);
 
-  bool doIsPrimary(AssetId id) => true;
-
-  void doApply(Transform transform) {
-    for (var entry in _entries) {
-      var parts = entry.split(":");
-      var logFn;
-      switch (parts[0]) {
-        case "error":   logFn = transform.logger.error; break;
-        case "warning": logFn = transform.logger.warning; break;
-        case "info":    logFn = transform.logger.info; break;
-        case "fine":    logFn = transform.logger.fine; break;
+  Future<bool> doIsPrimary(_) => new Future.value(true);
+
+  Future doApply(Transform transform) {
+    return newFuture(() {
+      for (var entry in _entries) {
+        var parts = entry.split(":");
+        var logFn;
+        switch (parts[0]) {
+          case "error":   logFn = transform.logger.error; break;
+          case "warning": logFn = transform.logger.warning; break;
+          case "info":    logFn = transform.logger.info; break;
+          case "fine":    logFn = transform.logger.fine; break;
+        }
+
+        logFn(parts[1].trim());
       }
-
-      logFn(parts[1].trim());
-    }
+    });
   }
 }