Sync UI: Add a flag to enable the new signin flow.

BUG=111244
TEST=none
R=csilv

Review URL: https://chromiumcodereview.appspot.com/10210003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@133759 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 2e55431..2f5a65b 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -643,6 +643,13 @@
     SINGLE_VALUE_TYPE(switches::kNoDiscardTabs)
   },
 #endif
+  {
+    "enable-sync-signing",
+    IDS_ENABLE_SYNC_SIGNIN_NAME,
+    IDS_ENABLE_SYNC_SIGNIN_DESCRIPTION,
+    kOsAll,
+    SINGLE_VALUE_TYPE(switches::kEnableSyncSignin)
+  },
 };
 
 const Experiment* experiments = kExperiments;