Cleanup: Use AUTH_SCHEME enum instead of a string.

net/http/http_auth_cache.cc

Index: net/http/http_auth_cache.cc
===================================================================
--- net/http/http_auth_cache.cc	(revision 70507)
+++ net/http/http_auth_cache.cc	(working copy)
@@ -68,7 +68,7 @@
 // Performance: O(n), where n is the number of realm entries.
 HttpAuthCache::Entry* HttpAuthCache::Lookup(const GURL& origin,
                                             const std::string& realm,
-                                            const std::string& scheme) {
+                                            HttpAuth::Scheme scheme) {
   CheckOriginIsValid(origin);
 
   // Linear scan through the realm entries.
@@ -104,7 +104,7 @@
 
 HttpAuthCache::Entry* HttpAuthCache::Add(const GURL& origin,
                                          const std::string& realm,
-                                         const std::string& scheme,
+                                         HttpAuth::Scheme scheme,
                                          const std::string& auth_challenge,
                                          const string16& username,
                                          const string16& password,
@@ -183,7 +183,7 @@
 
 bool HttpAuthCache::Remove(const GURL& origin,
                            const std::string& realm,
-                           const std::string& scheme,
+                           HttpAuth::Scheme scheme,
                            const string16& username,
                            const string16& password) {
   for (EntryList::iterator it = entries_.begin(); it != entries_.end(); ++it) {
@@ -201,7 +201,7 @@
 
 bool HttpAuthCache::UpdateStaleChallenge(const GURL& origin,
                                          const std::string& realm,
-                                         const std::string& scheme,
+                                         HttpAuth::Scheme scheme,
                                          const std::string& auth_challenge) {
   HttpAuthCache::Entry* entry = Lookup(origin, realm, scheme);
   if (!entry)