Add a SigninAllowed policy.

chrome/test/base/testing_profile.h

Index: chrome/test/base/testing_profile.h
diff --git a/chrome/test/base/testing_profile.h b/chrome/test/base/testing_profile.h
index 858f0f199544e5ae798cf3b441a7fb6ec9d97ef9..88b048eb00149a776446c0aedbe10752b7c1b2c3 100644
--- a/chrome/test/base/testing_profile.h
+++ b/chrome/test/base/testing_profile.h
@@ -210,6 +210,7 @@ class TestingProfile : public Profile {
   void set_incognito(bool incognito) { incognito_ = incognito; }
   // Assumes ownership.
   virtual void SetOffTheRecordProfile(Profile* profile);
+  virtual void SetOriginalProfile(Profile* profile);
   virtual Profile* GetOffTheRecordProfile() OVERRIDE;
   virtual void DestroyOffTheRecordProfile() OVERRIDE {}
   virtual bool HasOffTheRecordProfile() OVERRIDE;
@@ -340,6 +341,7 @@ class TestingProfile : public Profile {
 
   bool incognito_;
   scoped_ptr<Profile> incognito_profile_;
+  Profile* original_profile_;
 
   // Did the last session exit cleanly? Default is true.
   bool last_session_exited_cleanly_;