Add a SigninAllowed policy.

chrome/browser/profiles/profile.h

Index: chrome/browser/profiles/profile.h
diff --git a/chrome/browser/profiles/profile.h b/chrome/browser/profiles/profile.h
index 40ca85de73bb64ed48b0636ff06803141ee44de5..93e2898b210cd14321440f4d165846d4f4fda084 100644
--- a/chrome/browser/profiles/profile.h
+++ b/chrome/browser/profiles/profile.h
@@ -351,6 +351,10 @@ class Profile : public content::BrowserContext {
   // disabled or controlled by configuration management.
   bool IsSyncAccessible();
 
+  // Checks whether signin to Chrome is allowed by the user. Returns false if
+  // signin is disabled or controlled by configuration management.
+  bool IsSigninAllowed();

[sail, 2013/02/08 20:18:57]

Could we avoid adding this here? chrome/browser/signin is probably a better
place.

[Adrian Kuegel, 2013/02/11 16:47:30]

Yes, it can be avoided, it was just making the code at other places a bit
easier, because I didn't have to get the SigninManager first. But I removed it
here now, and changed the code at other places accordingly.

+
   // Send NOTIFICATION_PROFILE_DESTROYED for this Profile, if it has not
   // already been sent. It is necessary because most Profiles are destroyed by
   // ProfileDestroyer, but in tests, some are not.