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

ash/mus/bridge/wm_shell_mus.h

Index: ash/mus/bridge/wm_shell_mus.h
diff --git a/ash/mus/bridge/wm_shell_mus.h b/ash/mus/bridge/wm_shell_mus.h
index de6ef61cd636fd0809b6b350e82b074e08e38822..69086afd816ffab6fe6b70315e7dadfce61ad0d7 100644
--- a/ash/mus/bridge/wm_shell_mus.h
+++ b/ash/mus/bridge/wm_shell_mus.h
@@ -7,6 +7,7 @@
 
 #include <stdint.h>
 
+#include <map>
 #include <memory>
 #include <vector>
 
@@ -144,6 +145,10 @@ class WmShellMus : public WmShell, public ui::WindowTreeClientObserver {
 
   base::ObserverList<WmActivationObserver> activation_observers_;
 
+  // A cache of stub display info objects, used in absence of DisplayManager.
+  // TODO(mash): Get actual info from DisplayManager. http://crbug.com/622480.
+  mutable std::map<int64_t, display::ManagedDisplayInfo> display_info_map_;
+
   DISALLOW_COPY_AND_ASSIGN(WmShellMus);
 };