Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

pkg/compiler/lib/src/js_backend/runtime_types.dart

 // 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.
 
 part of js_backend;
 
 /// For each class, stores the possible class subtype tests that could succeed.
 abstract class TypeChecks {
   /// Get the set of checks required for class [element].
   Iterable<TypeCheck> operator[](ClassElement element);
@@ skipping 889 matching lines @@
  * substition for this check.
  */
 class TypeCheck {
   final ClassElement cls;
   final Substitution substitution;
   final int hashCode = (nextHash++) & 0x3fffffff;
   static int nextHash = 49;
 
   TypeCheck(this.cls, this.substitution);
 }