Hook up Chrome's wallpaper picker for mash.

chrome/browser/ui/ash/chrome_wallpaper_helper.cc

Index: chrome/browser/ui/ash/chrome_wallpaper_helper.cc
diff --git a/chrome/browser/ui/ash/chrome_wallpaper_helper.cc b/chrome/browser/ui/ash/chrome_wallpaper_helper.cc
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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.
+
+#include "chrome/browser/ui/ash/chrome_wallpaper_helper.h"
+
+#include "chrome/browser/chromeos/extensions/wallpaper_manager_util.h"
+
+ChromeWallpaperHelper::ChromeWallpaperHelper() {}
+
+ChromeWallpaperHelper::~ChromeWallpaperHelper() {}
+
+void ChromeWallpaperHelper::ProcessRequest(
+    mash::mojom::WallpaperHelperRequest request) {
+  bindings_.AddBinding(this, std::move(request));
+}
+
+void ChromeWallpaperHelper::OpenWallpaperManager() {
+  wallpaper_manager_util::OpenWallpaperManager();
+}