Install barback from a hosted source in all tests.

test/build/defaults_to_release_mode_test.dart

Index: test/build/defaults_to_release_mode_test.dart
diff --git a/test/build/defaults_to_release_mode_test.dart b/test/build/defaults_to_release_mode_test.dart
index 11199b7cc44336660ef42a06ccbab3f64813b00f..faa81d14f23a6f48246706b269adac321932ad1f 100644
--- a/test/build/defaults_to_release_mode_test.dart
+++ b/test/build/defaults_to_release_mode_test.dart
@@ -29,10 +29,13 @@ class ModeTransformer extends Transformer {
 
 main() {
    integration("defaults to release mode", () {
+     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)
@@ -42,8 +45,7 @@ main() {
        ])
      ]).create();
 
-     createLockFile('myapp', pkg: ['barback']);
-
+     pubGet();
      schedulePub(args: ["build"]);
 
      d.dir(appPath, [