Install barback from a hosted source in all tests.

test/transformer/asset_not_found_exceptions_are_detectable_test.dart

Index: test/transformer/asset_not_found_exceptions_are_detectable_test.dart
diff --git a/test/transformer/asset_not_found_exceptions_are_detectable_test.dart b/test/transformer/asset_not_found_exceptions_are_detectable_test.dart
index 3dfcfa469141e064cf048e6019e5d30d08af71f2..523ac4e8d5ead2044dcc8a367d462d343cb46e0c 100644
--- a/test/transformer/asset_not_found_exceptions_are_detectable_test.dart
+++ b/test/transformer/asset_not_found_exceptions_are_detectable_test.dart
@@ -39,10 +39,13 @@ class GetInputTransformer extends Transformer {
 
 main() {
   integration("AssetNotFoundExceptions are detectable", () {
+    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)
@@ -52,8 +55,7 @@ main() {
       ])
     ]).create();
 
-    createLockFile('myapp', pkg: ['barback']);
-
+    pubGet();
     var server = pubServe();
     requestShouldSucceed("foo.txt", JSON.encode({
       "package": "myapp",