Rename the global inference task and reduce it's API surface by introducing the

pkg/compiler/lib/src/types/forwarding_type_mask.dart

Index: pkg/compiler/lib/src/types/forwarding_type_mask.dart
diff --git a/pkg/compiler/lib/src/types/forwarding_type_mask.dart b/pkg/compiler/lib/src/types/forwarding_type_mask.dart
index 0e30bac477e7f01b8c59ce7423461c74b956491d..bc9ce155aee638bb0f8f82d49eb051f2313b1943 100644
--- a/pkg/compiler/lib/src/types/forwarding_type_mask.dart
+++ b/pkg/compiler/lib/src/types/forwarding_type_mask.dart
@@ -2,7 +2,7 @@
 // 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;
+part of masks;
 
 /**
  * A type mask that wraps an other one, and delegate all its