Support transformers that depend on other transformers.

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

Index: sdk/lib/_internal/pub/test/serve/runs_a_third_party_transformer_on_a_local_transformer_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/runs_a_third_party_transform_on_the_application_package_test.dart b/sdk/lib/_internal/pub/test/serve/runs_a_third_party_transformer_on_a_local_transformer_test.dart
similarity index 52%
copy from sdk/lib/_internal/pub/test/serve/runs_a_third_party_transform_on_the_application_package_test.dart
copy to sdk/lib/_internal/pub/test/serve/runs_a_third_party_transformer_on_a_local_transformer_test.dart
index 8185e560c8e976fb6f86db247d95fca190e7d1e5..b3073a84defcb3b9f144f4341386426b31a5c53c 100644
--- a/sdk/lib/_internal/pub/test/serve/runs_a_third_party_transform_on_the_application_package_test.dart
+++ b/sdk/lib/_internal/pub/test/serve/runs_a_third_party_transformer_on_a_local_transformer_test.dart
@@ -10,31 +10,33 @@ import 'utils.dart';
 
 main() {
   initConfig();
-  integration("runs a third-party transform on the application package", () {
+  integration("runs a third-party transformer on a local transformer", () {
     d.dir("foo", [
       d.libPubspec("foo", '1.0.0'),
       d.dir("lib", [
-        d.file("foo.dart", REWRITE_TRANSFORMER)
+        d.file("transformer.dart", dartTransformer('foo'))
       ])
     ]).create();
 
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
-        "dependencies": {"foo": {"path": "../foo"}},
-        "transformers": ["foo"]
+        "transformers": ["foo/transformer", "myapp/transformer"],
+        "dependencies": {"foo": {"path": "../foo"}}
       }),
+      d.dir("lib", [
+        d.file("transformer.dart", dartTransformer('myapp'))
+      ]),
       d.dir("web", [
-        d.file("foo.txt", "foo")
+        d.file("main.dart", 'const TOKEN = "main.dart";')
       ])
     ]).create();
 
-    createLockFile('myapp', {
-      'foo': '../foo'
-    }, pkg: ['barback']);
+    createLockFile('myapp', sandbox: ['foo'], pkg: ['barback']);
 
     startPubServe();
-    requestShouldSucceed("foo.out", "foo.out");
+    requestShouldSucceed("main.dart",
+        'const TOKEN = "((main.dart, foo), (myapp, foo))";');
     endPubServe();
   });
 }