Disabling extended desktop (by default).

ash/display/display_controller.cc

Index: ash/display/display_controller.cc
diff --git a/ash/display/display_controller.cc b/ash/display/display_controller.cc
index 456b831235a36e971c5e3bb6e08f7ee21f7567a8..c50c4b9a6d0af5313c0fba2af6b5fd241bfd4bcb 100644
--- a/ash/display/display_controller.cc
+++ b/ash/display/display_controller.cc
@@ -22,6 +22,10 @@
 
 namespace ash {
 namespace internal {
+namespace {
+// True if the extended desktop mode is enabled.
+bool extended_desktop_enabled = false;
+}  // namespace
 
 DisplayController::DisplayController()
     : secondary_display_layout_(RIGHT),
@@ -207,10 +211,14 @@ void DisplayController::OnDisplayRemoved(const gfx::Display& display) {
 
 // static
 bool DisplayController::IsExtendedDesktopEnabled(){
-  static bool extended_desktop_disabled =
+  return extended_desktop_enabled ||
       CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kAshExtendedDesktopDisabled);
-  return !extended_desktop_disabled;
+          switches::kAshExtendedDesktop);
+}
+
+// static
+void DisplayController::SetExtendedDesktopEnabled(bool enabled) {
+  extended_desktop_enabled = enabled;
 }
 
 aura::RootWindow* DisplayController::AddRootWindowForDisplay(