dart2js: fix dependency tracking for deferred loading when types are only used

tests/compiler/dart2js_extra/deferred_split_test.dart

+// Copyright (c) 2015, 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.
+
+/// Regression for issue 23853: we used to incorreclty split and put a type in a
+/// deferred hunk if the type was used explicitly in the deferred library and
+/// was used only in a generic type in the main library.
+library compiler.test.dart2js_extra.deferred_split_test;
+
+import 'deferred_split_lib1.dart';
+import 'deferred_split_lib2.dart' deferred as b;
+
+class TypeLiteral<T> {
+  Type get type => T;
+}
+
+main() {
+  // This line failed with a runtime error prior to the fix:
+  new TypeLiteral<A<Object>>().type;
+
+  b.loadLibrary().then((_) => b.createA());
+}