Support additional mash shelf alignments.

mash/wm/public/interfaces/shelf_layout.mojom

Index: mash/wm/public/interfaces/shelf_layout.mojom
diff --git a/mash/wm/public/interfaces/shelf_layout.mojom b/mash/wm/public/interfaces/shelf_layout.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..f146186f82d553dc906c63801d2dc12af4a6fbff
--- /dev/null
+++ b/mash/wm/public/interfaces/shelf_layout.mojom
@@ -0,0 +1,14 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module mash.wm.mojom;
+
+import "mash/shelf/public/interfaces/shelf_constants.mojom";
+
+// Used by mojo:ash_sysui to push the current shelf state to its layout manager.
+interface ShelfLayout {
+  // TODO: Update preferred sizes with alignment to avoid flicker during layout.
+  SetAlignment(mash.shelf.mojom.Alignment alignment);
+  SetAutoHideBehavior(mash.shelf.mojom.AutoHideBehavior auto_hide);
+};