Support loading transformer plugins from pub.

sdk/lib/_internal/pub/test/serve/runs_a_local_transform_on_the_application_package_test.dart

Index: sdk/lib/_internal/pub/test/serve/runs_a_local_transform_on_the_application_package_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/watch_modified_file_test.dart b/sdk/lib/_internal/pub/test/serve/runs_a_local_transform_on_the_application_package_test.dart
similarity index 53%
copy from sdk/lib/_internal/pub/test/serve/watch_modified_file_test.dart
copy to sdk/lib/_internal/pub/test/serve/runs_a_local_transform_on_the_application_package_test.dart
index 6cf610d3931dc93a811223b259603ed5ed0abe25..0ae9397a5ac3fbe04c5ae70c206c63a2477bd7a0 100644
--- a/sdk/lib/_internal/pub/test/serve/watch_modified_file_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/runs_a_local_transform_on_the_application_package_test.dart
@@ -10,25 +10,24 @@ import 'utils.dart';
 
 main() {
   initConfig();
-  integration("watches modifications to files", () {
+  integration("runs a local transform on the application package", () {
     d.dir(appPath, [
-      d.appPubspec(),
+      d.pubspec({
+        "name": "myapp",
+        "transformers": ["myapp/src/transformer"]
+      }),
+      d.dir("lib", [d.dir("src", [
+        d.file("transformer.dart", REWRITE_TRANSFORMER)
+      ])]),
       d.dir("web", [
-        d.file("index.html", "before")
+        d.file("foo.txt", "foo")
       ])
     ]).create();
 
-    startPubServe();
-    requestShouldSucceed("index.html", "before");
+    createLockFile('myapp', {}, pkg: ['barback']);
 
-    d.dir(appPath, [
-      d.dir("web", [
-        d.file("index.html", "after")
-      ])
-    ]).create();
-
-    waitForBuildSuccess();
-    requestShouldSucceed("index.html", "after");
+    startPubServe();
+    requestShouldSucceed("foo.out", "foo.out");
     endPubServe();
   });
 }