Add FakeDisplayDelegate for off device usage.

ui/display/display_switches.cc

Index: ui/display/display_switches.cc
diff --git a/ui/display/display_switches.cc b/ui/display/display_switches.cc
index 445b0c635900e693e5e5741da2349dd6f9be160e..6983a2ed81fbe60166ed25290b5996b025c52d13 100644
--- a/ui/display/display_switches.cc
+++ b/ui/display/display_switches.cc
@@ -10,6 +10,10 @@ namespace switches {
 // TODO(rjkroege): Some of these have an "ash" prefix. When ChromeOS startup
 // scripts have been updated, the leading "ash" prefix should be removed.
 
+// Specifies the initial display configuration for FakeDisplayDelegate, see
+// class for format details.
+const char kDisplayConfig[] = "display-config";
+
 // Overrides the device scale factor for the browser UI and the contents.
 const char kForceDeviceScaleFactor[] = "force-device-scale-factor";