Process DisplaySnapshots in PlatformScreen.

services/ui/ws/display_manager.h

Index: services/ui/ws/display_manager.h
diff --git a/services/ui/ws/display_manager.h b/services/ui/ws/display_manager.h
index 245154d304dd55643394feb4bd74092680cfb916..17ca01d6979687ac5b64237b6d3f8102a040ef2b 100644
--- a/services/ui/ws/display_manager.h
+++ b/services/ui/ws/display_manager.h
@@ -54,6 +54,10 @@ class DisplayManager : public UserIdTrackerObserver,
   Display* GetDisplayContaining(ServerWindow* window);
   const Display* GetDisplayContaining(const ServerWindow* window) const;
 
+  // Returns the display with the specified display id, or null if there is no
+  // display with that id.
+  Display* GetDisplayById(int64_t display_id);
+
   const WindowManagerDisplayRoot* GetWindowManagerDisplayRoot(
       const ServerWindow* window) const;
   // TODO(sky): constness here is wrong! fix!