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

pkg/compiler/lib/src/types/value_type_mask.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.
-
-part of types;
-
-class ValueTypeMask extends ForwardingTypeMask {
-  final TypeMask forwardTo;
-  final value;
-
-  ValueTypeMask(this.forwardTo, this.value);
-
-  TypeMask nullable() {
-    return isNullable
-        ? this
-        : new ValueTypeMask(forwardTo.nullable(), value);
-  }
-
-  TypeMask nonNullable() {
-    return isNullable
-        ? new ValueTypeMask(forwardTo.nonNullable(), value)
-        : this;
-  }
-
-  bool get isValue => true;
-
-  bool equalsDisregardNull(other) {
-    if (other is! ValueTypeMask) return false;
-    return super.equalsDisregardNull(other) && value == other.value;
-  }
-
-  TypeMask intersection(TypeMask other, ClassWorld classWorld) {
-    TypeMask forwardIntersection = forwardTo.intersection(other, classWorld);
-    if (forwardIntersection.isEmpty) return forwardIntersection;
-    return forwardIntersection.isNullable
-        ? nullable()
-        : nonNullable();
-  }
-
-  bool operator==(other) => super == other;
-
-  int get hashCode {
-    return computeHashCode(value, isNullable, forwardTo);
-  }
-
-  String toString() {
-    return 'Value mask: [$value] type: $forwardTo';
-  }
-}