Save and restore unified mode

ash/test/display_manager_test_api.cc

Index: ash/test/display_manager_test_api.cc
diff --git a/ash/test/display_manager_test_api.cc b/ash/test/display_manager_test_api.cc
index a52ec03f3e7fdc925d64f829cc4e761d72e3ddd0..751553dc2a726be79ca6728d05c338b00622c071 100644
--- a/ash/test/display_manager_test_api.cc
+++ b/ash/test/display_manager_test_api.cc
@@ -6,6 +6,7 @@
 
 #include <vector>
 
+#include "ash/ash_switches.h"
 #include "ash/display/display_info.h"
 #include "ash/display/display_manager.h"
 #include "ash/display/display_util.h"
@@ -13,6 +14,7 @@
 #include "ash/display/mouse_cursor_event_filter.h"
 #include "ash/display/unified_mouse_warp_controller.h"
 #include "ash/shell.h"
+#include "base/command_line.h"
 #include "base/strings/string_split.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window_event_dispatcher.h"
@@ -92,6 +94,14 @@ bool DisplayManagerTestApi::TestIfMouseWarpsAt(
   }
 }
 
+// static
+void DisplayManagerTestApi::EnableUnifiedDesktopForTest() {
+#if defined(OS_CHROMEOS)
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      switches::kAshEnableUnifiedDesktop);
+#endif
+}
+
 DisplayManagerTestApi::DisplayManagerTestApi(DisplayManager* display_manager)
     : display_manager_(display_manager) {}