Support transformers that depend on other transformers.

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

Index: sdk/lib/_internal/pub/test/serve/loads_a_diamond_transformer_dependency_graph_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/loads_a_diamond_transformer_dependency_graph_test.dart b/sdk/lib/_internal/pub/test/serve/loads_a_diamond_transformer_dependency_graph_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0dfd10f26df75f66b6bb2da577c024339fae19e3
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/serve/loads_a_diamond_transformer_dependency_graph_test.dart
@@ -0,0 +1,79 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library pub_tests;
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+
+main() {
+  initConfig();
+  integration("loads a diamond transformer dependency graph", () {
+    d.dir("top", [
+      d.pubspec({
+        "name": "top",
+        "version": "1.0.0"
+      }),
+      d.dir("lib", [
+        d.file("transformer.dart", dartTransformer('top')),
+      ])
+    ]).create();
+
+    d.dir("left", [
+      d.pubspec({
+        "name": "left",
+        "version": "1.0.0",
+        "transformers": ["top/transformer"],
+        "dependencies": {"top": {"path": "../top"}}
+      }),
+      d.dir("lib", [
+        d.file("transformer.dart", dartTransformer('left')),
+      ])
+    ]).create();
+
+    d.dir("right", [
+      d.pubspec({
+        "name": "right",
+        "version": "1.0.0",
+        "transformers": ["top/transformer"],
+        "dependencies": {"top": {"path": "../top"}}
+      }),
+      d.dir("lib", [
+        d.file("transformer.dart", dartTransformer('right')),
+      ])
+    ]).create();
+
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "transformers": [
+          "left/transformer",
+          "right/transformer",
+          "myapp/transformer"
+        ],
+        "dependencies": {
+          'left': {'path': '../left'},
+          'right': {'path': '../right'},
+        }
+      }),
+      d.dir("lib", [
+        d.file("transformer.dart", dartTransformer('myapp'))
+      ]),
+      d.dir("web", [
+        d.file("main.dart", 'const TOKEN = "main.dart";')
+      ])
+    ]).create();
+
+    createLockFile('myapp',
+        sandbox: ['top', 'left', 'right'],
+        pkg: ['barback']);
+
+    startPubServe();
+    requestShouldSucceed("main.dart",
+        'const TOKEN = "main.dart, left, top, right, top, myapp, left, top, '
+        'right, top";');
+    endPubServe();
+  });
+}