Hook up Chrome's wallpaper picker for mash.

mash/public/interfaces/wallpaper.mojom

+// 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();
+};