Hook up Chrome's wallpaper picker for mash.

ash/mus/user_wallpaper_delegate_mus.cc

+// 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 "ash/mus/user_wallpaper_delegate_mus.h"
+
+#include "ash/desktop_background/desktop_background_controller.h"
+#include "ash/shell.h"
+#include "components/wallpaper/wallpaper_layout.h"
+#include "mash/public/interfaces/wallpaper.mojom.h"
+#include "services/shell/public/cpp/connector.h"
+#include "skia/public/type_converters.h"
+#include "ui/views/mus/window_manager_connection.h"
+#include "ui/wm/core/window_animations.h"
+
+namespace ash {
+
+int UserWallpaperDelegateMus::GetAnimationType() {
+  return ::wm::WINDOW_VISIBILITY_ANIMATION_TYPE_FADE;
+}
+
+int UserWallpaperDelegateMus::GetAnimationDurationOverride() {
+  return 0;
+}
+
+void UserWallpaperDelegateMus::SetAnimationDurationOverride(
+    int animation_duration_in_ms) {
+  NOTIMPLEMENTED();
+}
+
+bool UserWallpaperDelegateMus::ShouldShowInitialAnimation() {
+  return false;
+}
+
+void UserWallpaperDelegateMus::UpdateWallpaper(bool clear_cache) {
+  NOTIMPLEMENTED();
+}
+
+void UserWallpaperDelegateMus::InitializeWallpaper() {
+  // No action required; ChromeBrowserMainPartsChromeos inits WallpaperManager.

[msw, 2016/05/19 19:28:51]

This is sufficient from my local testing, but I could hook up an
ash_sysui->chrome init call for redundancy / explicit behavior if desired.
Here's the existing codepath that initialize the wallpaper correctly (afaict) in
mash with or without --login-manager:

#1 chromeos::WallpaperManager::PendingWallpaper::PendingWallpaper()
#2 chromeos::WallpaperManager::GetPendingWallpaper()
#3 chromeos::WallpaperManager::ScheduleSetUserWallpaper()
#4 wallpaper::WallpaperManagerBase::SetUserWallpaperNow()
#5 chromeos::ChromeUserManagerImpl::RegularUserLoggedInAsEphemeral()
#6 user_manager::UserManagerBase::UserLoggedIn()
#7 chromeos::ChromeBrowserMainPartsChromeos::PreProfileInit()
#8 ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#9 ChromeBrowserMainParts::PreMainMessageLoopRun()
#10 chromeos::ChromeBrowserMainPartsChromeos::PreMainMessageLoopRun()
#11 content::BrowserMainLoop::PreMainMessageLoopRun()

+}
+
+void UserWallpaperDelegateMus::OpenSetWallpaperPage() {
+  mash::mojom::WallpaperHelperPtr wallpaper_helper;
+  auto* connector = views::WindowManagerConnection::Get()->connector();
+  connector->ConnectToInterface("exe:chrome", &wallpaper_helper);
+  wallpaper_helper->OpenWallpaperManager();
+}
+
+bool UserWallpaperDelegateMus::CanOpenSetWallpaperPage() {
+  return true;
+}
+
+void UserWallpaperDelegateMus::OnWallpaperAnimationFinished() {}
+
+void UserWallpaperDelegateMus::OnWallpaperBootAnimationFinished() {}
+
+void UserWallpaperDelegateMus::SetWallpaper(skia::mojom::BitmapPtr wallpaper,
+                                            int32_t layout) {
+  const SkBitmap bitmap = wallpaper.To<SkBitmap>();
+  if (bitmap.isNull())
+    return;
+  gfx::ImageSkia image = gfx::ImageSkia::CreateFrom1xBitmap(bitmap);
+  ash::Shell::GetInstance()->desktop_background_controller()->SetWallpaperImage(
+      image, static_cast<wallpaper::WallpaperLayout>(layout));
+}
+
+}  // namespace ash