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

tests/lib/mirrors/library_imports_prefixed_show_hide_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_show_hide.dart';
-
-test(MirrorSystem mirrors) {
-  LibraryMirror prefixed_show_hide = mirrors.findLibrary(#library_imports_prefixed_show_hide);
-  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_show_hide.libraryDependencies.map((dep) => dep.targetLibrary));
-
-  Expect.stringEquals(
-      'import dart.core\n'
-      'import library_imports_a as prefixa\n'
-      ' show somethingFromA\n'
-      'import library_imports_b as prefixb\n'
-      ' hide somethingFromB\n',
-      stringifyDependencies(prefixed_show_hide));
-}
-
-main() {
-  test(currentMirrorSystem());
-}