Added chrome switch that lets tests override URL path, moved GAIA auth extension from CrOS

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 352c6dd5f7eb25a24ae5480f2e43bedea91edd08..85637e8de0d87e8bd8a733d68ebfbaa73d902c27 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -700,6 +700,11 @@ const char kForceAppsPromoVisible[]         = "force-apps-promo-visible";
 // omitted. The default value is "www.google.com".
 const char kGaiaHost[]                      = "gaia-host";
 
+// Specifies the path prefix for GAIA authentication URL. It should be used
+// for testing in cases where authentication path prefix differs from the one
+// used in production.
+const char kGaiaUrlPath[]                   = "gaia-url-path";
+
 // Enables using GAIA information to populate profile name and icon.
 const char kGaiaProfileInfo[]               = "gaia-profile-info";