Hook up Chrome's wallpaper picker for mash.

mash/public/interfaces/wallpaper.mojom

Index: mash/public/interfaces/wallpaper.mojom
diff --git a/mash/public/interfaces/wallpaper.mojom b/mash/public/interfaces/wallpaper.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..de24cc0f81c69bddd6e31576c4726fa955ab3aef
--- /dev/null
+++ b/mash/public/interfaces/wallpaper.mojom
@@ -0,0 +1,17 @@
+// 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.mojom;
+
+import "skia/public/interfaces/bitmap.mojom";
+
+// Used by Chrome to set the wallpaper displayed by Mash.
+interface WallpaperController {
+  SetWallpaper(skia.mojom.Bitmap wallpaper, int32 layout);
+};
+
+// Used by Mash to trigger Chrome's wallpaper picker functionality.
+interface WallpaperHelper {
+  OpenWallpaperManager();
+};