Fix filtering out .dart files in release mode.

sdk/lib/_internal/pub/test/build/dart2js_finds_imports_across_packages_test.dart

Index: sdk/lib/_internal/pub/test/build/dart2js_finds_imports_across_packages_test.dart
diff --git a/sdk/lib/_internal/pub/test/build/dart2js_finds_imports_across_packages_test.dart b/sdk/lib/_internal/pub/test/build/dart2js_finds_imports_across_packages_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0778ab15ab8fe600e971e9156f508a44fbffa5c2
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/build/dart2js_finds_imports_across_packages_test.dart
@@ -0,0 +1,59 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS 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.
+
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+
+main() {
+  initConfig();
+
+  // This is a regression test for https://dartbug.com/15183. The code that
+  // stripped .dart files from release builds was in the forwarding transformer,
+  // and that transformer was applied to all loaded packages. That meant that
+  // if the root package imported a .dart file from another package, the
+  // forwarding transformer in that package would remove the file before
+  // dart2js could find it when compiling the entrypoint in the root package.
+
+  integration("dart2js can find imports across packages", () {
+    // Dart2js can take a long time to compile dart code, so we increase the
+    // timeout to cope with that.
+    currentSchedule.timeout *= 3;
+
+    d.dir("foo", [
+      d.libPubspec("foo", "0.0.1"),
+      d.dir("lib", [
+        d.file("foo.dart",
+            """
+            library foo;
+            foo() => 'foo';
+            """)
+      ])
+    ]).create();
+
+    d.dir(appPath, [
+      d.appPubspec({
+        "foo": {"path": "../foo"}
+      }),
+      d.dir("web", [
+        d.file("main.dart",
+            """
+            import 'package:foo/foo.dart';
+            main() => print(foo());
+            """)
+      ])
+    ]).create();
+
+    schedulePub(args: ["build"],
+        output: new RegExp(r"Built 1 file!"),
+        exitCode: 0);
+
+    d.dir(appPath, [
+      d.dir('build', [
+        d.matcherFile('main.dart.js', isNot(isEmpty))
+      ])
+    ]).validate();
+  });
+}