sdk files reorganization to make dart2js a proper package

sdk/lib/_internal/compiler/js_lib/mirrors_patch.dart

-// Copyright (c) 2012, 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.
-
-// Patch library for dart:mirrors.
-
-import 'dart:_js_helper' show patch;
-import 'dart:_js_mirrors' as js;
-
-@patch
-class MirrorSystem {
-  @patch
-  static String getName(Symbol symbol) => js.getName(symbol);
-
-  @patch
-  static Symbol getSymbol(String name, [LibraryMirror library]) {
-    return js.getSymbol(name, library);
-  }
-}
-
-@patch
-MirrorSystem currentMirrorSystem() => js.currentJsMirrorSystem;
-
-@patch
-InstanceMirror reflect(Object reflectee) => js.reflect(reflectee);
-
-@patch
-ClassMirror reflectClass(Type key) {
-  if (key is! Type || key == dynamic) {
-    throw new ArgumentError('$key does not denote a class');
-  }
-  TypeMirror tm = reflectType(key);
-  if (tm is! ClassMirror) {
-    throw new ArgumentError("$key does not denote a class");
-  }
-  return (tm as ClassMirror).originalDeclaration;
-}
-
-@patch
-TypeMirror reflectType(Type key) {
-  if (key == dynamic) {
-    return currentMirrorSystem().dynamicType;
-  }
-  return js.reflectType(key);
-}