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

pkg/compiler/lib/src/ssa/types.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.
 
 part of ssa;
 
 class TypeMaskFactory {
   static TypeMask fromInferredType(TypeMask mask, Compiler compiler) {
     JavaScriptBackend backend = compiler.backend;
     if (mask == null) return backend.dynamicType;
@@ skipping 50 matching lines @@
       return backend.nullType;
     } else if (type.element == compiler.nullClass) {
       return backend.nullType;
     } else if (type.treatAsDynamic) {
       return backend.dynamicType;
     } else {
       return new TypeMask.nonNullSubtype(type.element, classWorld);
     }
   }
 }