Hook up Chrome's wallpaper picker for mash.

ash/mus/public/interfaces/wallpaper.mojom

Index: ash/mus/public/interfaces/wallpaper.mojom
diff --git a/ash/mus/public/interfaces/wallpaper.mojom b/ash/mus/public/interfaces/wallpaper.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..741bd237064e4fb3c804949ca23da77ee7262b72
--- /dev/null
+++ b/ash/mus/public/interfaces/wallpaper.mojom
@@ -0,0 +1,20 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.

[sky, 2016/05/21 16:09:20]

Please add an OWNERS file for this directory that has all the security guys as
owners for the mojom files. See
https://chromium.googlesource.com/chromium/src/+/master/components/mus/public...
for an example of what I mean.

[msw, 2016/05/24 18:45:42]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module ash.mus.mojom;
+
+import "skia/public/interfaces/bitmap.mojom";
+
+// These values match wallpaper::WallpaperLayout.
+enum WallpaperLayout { CENTER, CENTER_CROPPED, STRETCH, TILE, };
+
+// Used by Chrome to set the wallpaper displayed by ash_sysui.
+interface WallpaperController {
+  SetWallpaper(skia.mojom.Bitmap wallpaper, WallpaperLayout layout);
+};
+
+// Used by ash_sysui to trigger Chrome's wallpaper picker functionality.
+interface WallpaperManager {
+  OpenWallpaperManager();

[sky, 2016/05/21 16:09:20]

nit: The 'WallpaperManager' here is a bit redundant. How about Open()?

[msw, 2016/05/24 18:45:42]

Done.

+};