Install barback from a hosted source in all tests.

test/serve/allows_arbitrary_modes_test.dart

Index: test/serve/allows_arbitrary_modes_test.dart
diff --git a/test/serve/allows_arbitrary_modes_test.dart b/test/serve/allows_arbitrary_modes_test.dart
index 531670e6348d6357de8f935053cb53dfe42204da..f76e7d410f8c19fa7ad21663ac42818c8876e638 100644
--- a/test/serve/allows_arbitrary_modes_test.dart
+++ b/test/serve/allows_arbitrary_modes_test.dart
@@ -30,10 +30,13 @@ class ModeTransformer extends Transformer {
 
 main() {
   integration("allows user-defined mode names", () {
+    serveBarback();
+
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
-        "transformers": ["myapp/src/transformer"]
+        "transformers": ["myapp/src/transformer"],
+        "dependencies": {"barback": "any"}
       }),
       d.dir("lib", [d.dir("src", [
         d.file("transformer.dart", TRANSFORMER)
@@ -43,8 +46,7 @@ main() {
       ])
     ]).create();
 
-    createLockFile('myapp', pkg: ['barback']);
-
+    pubGet();
     pubServe(args: ["--mode", "depeche"]);
     requestShouldSucceed("foo.out", "depeche");
     endPubServe();