Support for auth code based authentication flow for both app and web UI driven flow.

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 55c12558650ee0e750c3038dc1a8f26778fc73a9..a05035c0ed3e17d26e14dbffa84ea18784f3de77 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -93,6 +93,9 @@ const char kAppsGalleryURL[]                = "apps-gallery-url";
 // The update url used by gallery/webstore extensions.
 const char kAppsGalleryUpdateURL[]          = "apps-gallery-update-url";
 
+// Value of GAIA auth code for --force-app-mode.
+const char kAppModeAuthCode[]               = "app-mode-auth-code";
+
 // Value of OAuth2 refresh token for --force-app-mode.
 const char kAppModeOAuth2Token[]            = "app-mode-oauth-token";