Add support for clearing the HTTP auth cache.

net/http/http_auth_cache.h

Index: net/http/http_auth_cache.h
diff --git a/net/http/http_auth_cache.h b/net/http/http_auth_cache.h
index 707a571db96c1faacaa957521a10af4574a33cbb..1867295ddd6141ce062fa6aa1dcc3afeb2aca7bb 100644
--- a/net/http/http_auth_cache.h
+++ b/net/http/http_auth_cache.h
@@ -163,6 +163,9 @@ class NET_EXPORT_PRIVATE HttpAuthCache {
               HttpAuth::Scheme scheme,
               const AuthCredentials& credentials);
 
+  // Clears the cache.
+  void Clear();
+
   // Updates a stale digest entry on server |origin| for realm |realm| and
   // scheme |scheme|. The cached auth challenge is replaced with
   // |auth_challenge| and the nonce count is reset.