Reapply "Access to imports in the VM's runtime mirrors. Extend test coverage of the source mirrors."

tests/lib/mirrors/library_imports_prefixed_test.dart

+// Copyright (c) 2014, 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.
+
+library test.library_imports;
+
+import 'dart:mirrors';
+import 'package:expect/expect.dart';
+import 'stringify.dart';
+
+import 'library_imports_prefixed.dart';
+
+test(MirrorSystem mirrors) {
+  LibraryMirror prefixed = mirrors.findLibrary(#library_imports_prefixed);
+  LibraryMirror a = mirrors.findLibrary(#library_imports_a);
+  LibraryMirror b = mirrors.findLibrary(#library_imports_b);
+  LibraryMirror core = mirrors.findLibrary(#dart.core);
+
+  Expect.setEquals([a, b, core],
+                   prefixed.libraryDependencies.map((dep) => dep.targetLibrary));
+
+  Expect.stringEquals(
+      'import dart.core\n'
+      'import library_imports_a as prefixa\n'
+      'import library_imports_b as prefixb\n',
+      stringifyDependencies(prefixed));
+}
+
+main() {
+  test(currentMirrorSystem());
+}