mash: Port sysui's WallpaperDelegateMus to mojo:ash.

ash/common/wallpaper/wallpaper_view.cc

Index: ash/common/wallpaper/wallpaper_view.cc
diff --git a/ash/common/wallpaper/wallpaper_view.cc b/ash/common/wallpaper/wallpaper_view.cc
index db52e79d5e354b378ef167c8a9dda59ff38b3eaf..35c27ce7f77ebba3c6b8f8ddafd583f620f72931 100644
--- a/ash/common/wallpaper/wallpaper_view.cc
+++ b/ash/common/wallpaper/wallpaper_view.cc
@@ -44,9 +44,14 @@ class LayerControlView : public views::View {
     // wallpaper view such as an overview mode shield.
     window->GetParent()->StackChildAtBottom(window);
     display::Display display = window->GetDisplayNearestWindow();
+
+    // TODO(mash): Mash returns a fake ManagedDisplayInfo. crbug.com/622480
+    float ui_scale = 1.f;
     display::ManagedDisplayInfo info =
         WmShell::Get()->GetDisplayInfo(display.id());
-    float ui_scale = info.GetEffectiveUIScale();
+    if (info.id() == display.id())
+      ui_scale = info.GetEffectiveUIScale();
+
     gfx::Size rounded_size =
         gfx::ScaleToFlooredSize(display.size(), 1.f / ui_scale);
     DCHECK_EQ(1, child_count());