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
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+// 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;

[sky, 2016/05/20 22:32:19]

The interfaces in here are intended for use by all mash apps, but the interfaces
you have here are specific to the sysui. I think they should move to
ash/mus/public/interfaces. ash/mus should really be in mash/sysui, which would
make this cleaner. I filed 613727 to rename ash/mus to ash/sysui, or bite the
bullet and move it to mash/sysui.

[msw, 2016/05/21 00:30:34]

Moved to ash/mus/public/interfaces... Maybe you can let me land this before we
move ash/mus, so I don't have to rebase?

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

Yes, sorry, I didn't mean you need to move everything before landing this. The
rename/move can happen at a later time.

+
+import "skia/public/interfaces/bitmap.mojom";
+
+// Used by Chrome to set the wallpaper displayed by ash_sysui.
+interface WallpaperController {
+  // Set the wallpaper image and the wallpaper::WallpaperLayout |layout|.
+  SetWallpaper(skia.mojom.Bitmap wallpaper, int32 layout);

[sky, 2016/05/20 22:32:19]

Don't we want to define WallpaperLayout in mojom?

[msw, 2016/05/21 00:30:35]

I guess; Done.

+};
+
+// Used by ash_sysui to trigger Chrome's wallpaper picker functionality.
+interface WallpaperHelper {

[sky, 2016/05/20 22:32:19]

Should the interface be named WallpaperManager?

[msw, 2016/05/21 00:30:35]

Heh, I had that but then though it was silly; Done.

+  OpenWallpaperManager();
+};