Add WindowPinType property on arua::Window

ash/public/interfaces/window_pin_type.mojom

Index: ash/public/interfaces/window_pin_type.mojom
diff --git a/ash/public/interfaces/window_pin_type.mojom b/ash/public/interfaces/window_pin_type.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..15e2dcef3329a39c495a7cbaa4d1564abf813def
--- /dev/null
+++ b/ash/public/interfaces/window_pin_type.mojom
@@ -0,0 +1,20 @@
+// Copyright 2017 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 ash.mojom;
+
+// The window's pin type enum.
+enum WindowPinType {
+  NONE,
+
+  // The window is pinned on top of other windows.
+  PINNED,
+
+  // The window is pinned on top of other windows. It is similar to
+  // PINNED but does not allow user to exit the mode by shortcut key.
+  TRUSTED_PINNED,
+};
+
+// The window's pin type. Maps to ash::aura::kWindowPinTypeKey.
+const string kWindowPinType_Property = "ash:window-pin-type";