Hook up Chrome's wallpaper picker for mash.

ash/desktop_background/desktop_background_controller.cc

 // Copyright (c) 2012 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/desktop_background/desktop_background_controller.h"
 
 #include "ash/ash_switches.h"
 #include "ash/desktop_background/desktop_background_controller_observer.h"
 #include "ash/desktop_background/desktop_background_view.h"
 #include "ash/desktop_background/desktop_background_widget_controller.h"
@@ skipping 143 matching lines @@
     if (desktop_background_mode_ == BACKGROUND_IMAGE &&
         current_wallpaper_.get())
       UpdateWallpaper(true /* clear cache */);
   }
 
   InstallDesktopController(root_window);
 }
 
 // static
 gfx::Size DesktopBackgroundController::GetMaxDisplaySizeInNative() {
+  // Return an empty size for test environments where the screen is null.

[James Cook, 2016/05/20 20:47:13]

Is this for mus-only tests? The old code would crash is Screen::GetScreen() was
null.

[msw, 2016/05/20 21:31:49]

No, it's not mus-only tests. This is the crash we were seeing in the prior patch
set; it was only exposed because I removed some other early returns when there's
no ash::Shell instance. We want to support the lack of an ash::Shell instance
here for uses by Chrome in mash, so I found that the lack of a display::Screen
instance was a better indicator for tests (hopefully for mus and non-mus
tests...)

+  if (!display::Screen::GetScreen())
+    return gfx::Size();
+
   int width = 0;
   int height = 0;
-  std::vector<display::Display> displays =
-      display::Screen::GetScreen()->GetAllDisplays();
-  DisplayManager* display_manager = Shell::GetInstance()->display_manager();
-
-  for (std::vector<display::Display>::iterator iter = displays.begin();
-       iter != displays.end(); ++iter) {
+  DisplayManager* display_manager =
+      Shell::HasInstance() ? Shell::GetInstance()->display_manager() : nullptr;
+  for (auto display : display::Screen::GetScreen()->GetAllDisplays()) {

[James Cook, 2016/05/20 20:47:13]

optional: Did you want to copy each Display object or use auto& ? Actually, this
might be clearer without auto, since you know the type and it isn't a long
iterator type.

(Oh, and I think the following code is much clearer with the |display| variable,
thanks.)

[msw, 2016/05/20 21:31:49]

Changed to auto&, display::Display& adds a line break :p

     // Don't use size_in_pixel because we want to use the native pixel size.
+    // TODO(msw): Fix this for Mash/Mus; see http://crbug.com/613657.
     gfx::Size size_in_pixel =
-        display_manager->GetDisplayInfo(iter->id()).bounds_in_native().size();
-    if (iter->rotation() == display::Display::ROTATE_90 ||
-        iter->rotation() == display::Display::ROTATE_270) {
+        display_manager
+            ? display_manager->GetDisplayInfo(display.id())
+                  .bounds_in_native()
+                  .size()
+            : display.size();
+    if (display.rotation() == display::Display::ROTATE_90 ||
+        display.rotation() == display::Display::ROTATE_270) {
       size_in_pixel = gfx::Size(size_in_pixel.height(), size_in_pixel.width());
     }
     width = std::max(size_in_pixel.width(), width);
     height = std::max(size_in_pixel.height(), height);
   }
   return gfx::Size(width, height);
 }
 
 bool DesktopBackgroundController::WallpaperIsAlreadyLoaded(
     const gfx::ImageSkia& image,
@@ skipping 89 matching lines @@
                 : kShellWindowId_DesktopBackgroundContainer;
 }
 
 void DesktopBackgroundController::UpdateWallpaper(bool clear_cache) {
   current_wallpaper_.reset(NULL);
   ash::Shell::GetInstance()->user_wallpaper_delegate()->UpdateWallpaper(
       clear_cache);
 }
 
 }  // namespace ash