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

pkg/compiler/lib/src/types/map_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;
 
 /**
  * A [MapTypeMask] is a [TypeMask] for a specific allocation
  * site of a map (currently only internal Map class) that will get specialized
  * once the [TypeGraphInferrer] phase finds a key and/or value type for it.
@@ skipping 100 matching lines @@
 
   int get hashCode {
     return computeHashCode(
         allocationNode, isNullable, keyType, valueType, forwardTo);
   }
 
   String toString() {
     return 'Map mask: [$keyType/$valueType] type: $forwardTo';
   }
 }