Hook up Chrome's wallpaper picker for mash.

chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc

Index: chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
diff --git a/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc b/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
index eac4ab8f45341ff25769a07253a02f001113e7dc..193b6f0b12afe1ef226dde829e2432cf78b0917d 100644
--- a/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
+++ b/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
@@ -57,6 +57,10 @@
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/common/content_switches.h"
+#include "content/public/common/mojo_shell_connection.h"
+#include "mash/public/interfaces/wallpaper.mojom.h"
+#include "services/shell/public/cpp/connector.h"
+#include "skia/public/type_converters.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/codec/jpeg_codec.h"
 #include "ui/gfx/image/image_skia_operations.h"
@@ -172,6 +176,24 @@ void SetKnownUserWallpaperFilesId(
                                           wallpaper_files_id.id());
 }
 
+// A helper to set the wallpaper image for Ash and Mash.
+void SetWallpaper(const gfx::ImageSkia& image,
+                  wallpaper::WallpaperLayout layout) {
+  if (ash::Shell::HasInstance() && !ash::Shell::GetInstance()->in_mus()) {
+    ash::Shell::GetInstance()
+        ->desktop_background_controller()
+        ->SetWallpaperImage(image, layout);
+  } else {
+    shell::Connector* connector =
+        content::MojoShellConnection::Get()->GetConnector();
+    mash::mojom::WallpaperControllerPtr wallpaper_controller;
+    connector->ConnectToInterface("mojo:ash_sysui", &wallpaper_controller);
+    wallpaper_controller->SetWallpaper(
+        skia::mojom::Bitmap::From(*image.bitmap()),
+        static_cast<int32_t>(layout));
+  }
+}
+
 }  // namespace
 
 // This is "wallpaper either scheduled to load, or loading right now".
@@ -202,8 +224,7 @@ class WallpaperManager::PendingWallpaper :
   // There are 4 cases in SetUserWallpaper:
   // 1) gfx::ImageSkia is found in cache.
   //    - Schedule task to (probably) resize it and install:
-  //    call ash::Shell::GetInstance()->desktop_background_controller()->
-  //          SetCustomWallpaper(user_wallpaper, layout);
+  //    call SetWallpaper(user_wallpaper, layout);
   // 2) WallpaperInfo is found in cache
   //    - need to LoadWallpaper(), resize and install.
   // 3) wallpaper path is not NULL, load image URL, then resize, etc...
@@ -257,9 +278,7 @@ class WallpaperManager::PendingWallpaper :
     if (default_) {
       manager->DoSetDefaultWallpaper(account_id_, std::move(on_finish_));
     } else if (!user_wallpaper_.isNull()) {
-      ash::Shell::GetInstance()
-          ->desktop_background_controller()
-          ->SetWallpaperImage(user_wallpaper_, info_.layout);
+      SetWallpaper(user_wallpaper_, info_.layout);
     } else if (!wallpaper_path_.empty()) {
       manager->task_runner_->PostTask(
           FROM_HERE,
@@ -598,11 +617,6 @@ void WallpaperManager::DoSetDefaultWallpaper(
   if (user_manager::UserManager::Get()->IsLoggedInAsKioskApp())
     return;
   wallpaper_cache_.erase(account_id);
-  // Some browser tests do not have a shell instance. As no wallpaper is needed
-  // in these tests anyway, avoid loading one, preventing crashes and speeding
-  // up the tests.
-  if (!ash::Shell::HasInstance())
-    return;
 
   WallpaperResolution resolution = GetAppropriateResolution();
   const bool use_small = (resolution == WALLPAPER_RESOLUTION_SMALL);
@@ -643,8 +657,7 @@ void WallpaperManager::DoSetDefaultWallpaper(
       default_wallpaper_image_->image().height() == 1)
     layout = wallpaper::WALLPAPER_LAYOUT_STRETCH;
 
-  ash::Shell::GetInstance()->desktop_background_controller()->SetWallpaperImage(
-      default_wallpaper_image_->image(), layout);
+  SetWallpaper(default_wallpaper_image_->image(), layout);
 }
 
 void WallpaperManager::SetUserWallpaperInfo(const AccountId& account_id,
@@ -959,11 +972,8 @@ void WallpaperManager::OnWallpaperDecoded(
   // Update the image, but keep the path which was set earlier.
   wallpaper_cache_[account_id].second = user_image->image();
 
-  if (update_wallpaper) {
-    ash::Shell::GetInstance()
-        ->desktop_background_controller()
-        ->SetWallpaperImage(user_image->image(), layout);
-  }
+  if (update_wallpaper)
+    SetWallpaper(user_image->image(), layout);
 }
 
 void WallpaperManager::StartLoad(const AccountId& account_id,
@@ -1068,8 +1078,7 @@ void WallpaperManager::OnDefaultWallpaperDecoded(
     MovableOnDestroyCallbackHolder on_finish,
     std::unique_ptr<user_manager::UserImage> user_image) {
   *result_out = std::move(user_image);
-  ash::Shell::GetInstance()->desktop_background_controller()->SetWallpaperImage(
-      (*result_out)->image(), layout);
+  SetWallpaper((*result_out)->image(), layout);
 }
 
 void WallpaperManager::StartLoadAndSetDefaultWallpaper(