Adding about:flags option to enable guest mode.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index be29824da375ae8f22f293a9084444bc2566d848..405a54fdbb0210e68c299be99416a4a2d7eed23f 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -485,6 +485,9 @@ const char kEnableContacts[]                = "enable-contacts";
 // Enables web developers to create apps for Chrome without using crx packages.
 const char kEnableCrxlessWebApps[]          = "enable-crxless-web-apps";
 
+// Enables desktop guest mode.
+const char kEnableDesktopGuestMode[]        = "enable-desktop-guest-mode";
+
 // If true devtools experimental settings are enabled.
 const char kEnableDevToolsExperiments[]     = "enable-devtools-experiments";