Remove HttpAuth::Scheme enum in favor of a string.

net/http/http_auth_handler.h

Index: net/http/http_auth_handler.h
diff --git a/net/http/http_auth_handler.h b/net/http/http_auth_handler.h
index 638bb44aed3dba4953c362ba9b5484146d706617..2c002c51735ac7ed7f6ed29bd06188ad08bf231d 100644
--- a/net/http/http_auth_handler.h
+++ b/net/http/http_auth_handler.h
@@ -76,7 +76,7 @@ class NET_EXPORT_PRIVATE HttpAuthHandler {
                         std::string* auth_token);
 
   // The authentication scheme as an enumerated value.
-  HttpAuth::Scheme auth_scheme() const {
+  std::string auth_scheme() const {
     return auth_scheme_;
   }
 
@@ -162,7 +162,7 @@ class NET_EXPORT_PRIVATE HttpAuthHandler {
                                     std::string* auth_token) = 0;
 
   // The auth-scheme as an enumerated value.
-  HttpAuth::Scheme auth_scheme_;
+  std::string auth_scheme_;
 
   // The realm, encoded as UTF-8. Used by "basic" and "digest".
   std::string realm_;