[net/http auth] Use strings to identify authentication schemes.

net/base/auth.h

Index: net/base/auth.h
diff --git a/net/base/auth.h b/net/base/auth.h
index 62a59c8f9fdad03a834a37ef4027313b43492f90..8dee1dbdece57ad12beabeb335d8ffe74d6edb0b 100644
--- a/net/base/auth.h
+++ b/net/base/auth.h
@@ -30,8 +30,7 @@ class NET_EXPORT AuthChallengeInfo :
   // The service issuing the challenge.
   HostPortPair challenger;
 
-  // The authentication scheme used, such as "basic" or "digest". If the
-  // |source| is FTP_SERVER, this is an empty string. The encoding is ASCII.
+  // The authentication scheme used, such as "basic" or "digest".
   std::string scheme;
 
   // The realm of the challenge. May be empty. The encoding is UTF-8.
@@ -89,6 +88,8 @@ enum AuthState {
   AUTH_STATE_CANCELED
 };
 
+// TODO(asanka): This is only used by URLRequestFtpJob. Get rid of this and move
+// the functionality to that class. http://crbug.com/529319
 class AuthData : public base::RefCountedThreadSafe<AuthData> {
  public:
   AuthState state;  // whether we need, have, or gave up on authentication.