Handle modified displays in mustash.

services/ui/public/interfaces/display/test_display_controller.mojom

Index: services/ui/public/interfaces/display/test_display_controller.mojom
diff --git a/services/ui/public/interfaces/display/test_display_controller.mojom b/services/ui/public/interfaces/display/test_display_controller.mojom
index adebf27b24f92be47a901c8122b8b5c3c867ab32..78c820e024bb917b5d155d7548d8f550f3adf22d 100644
--- a/services/ui/public/interfaces/display/test_display_controller.mojom
+++ b/services/ui/public/interfaces/display/test_display_controller.mojom
@@ -12,4 +12,7 @@ interface TestDisplayController {
   // a second display is added. If there is more than one display then the last
   // display is removed. 
   ToggleAddRemoveDisplay();
+
+  // Toggles the primary display resolution size.
+  ToggleDisplayResolution();
 };