Move RegisterTokenResponse to private

This CL is a part of moving access token management to
OAuth2AccessTokenManager.

It moves RegisterTokenResponse to private since it's
only used by OAuth2AccessTokenManager::Fetcher which is
a nested class in OAuth2AccessTokenManager.

Bug: 967598
Change-Id: Ic51db4d938f955e920a33d00a6f74e07f88a8763
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1731029Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Julie Jeongeun Kim <jkim@igalia.com>
Cr-Commit-Position: refs/heads/master@{#683106}

google_apis/gaia/oauth2_access_token_manager.h

@@ -225,13 +225,6 @@ class OAuth2AccessTokenManager {
       const std::string& client_secret,
       const ScopeSet& scopes);
 
-  // Add a new entry to the cache.
-  void RegisterTokenResponse(
-      const std::string& client_id,
-      const CoreAccountId& account_id,
-      const ScopeSet& scopes,
-      const OAuth2AccessTokenConsumer::TokenResponse& token_response);
-
   // Returns a currently valid OAuth2 access token for the given set of scopes,
   // or NULL if none have been cached. Note the user of this method should
   // ensure no entry with the same |client_scopes| is added before the usage of
@@ -312,6 +305,13 @@ class OAuth2AccessTokenManager {
       RequestImpl* request,
       const RequestParameters& client_scopes);
 
+  // Add a new entry to the cache.
+  void RegisterTokenResponse(
+      const std::string& client_id,
+      const CoreAccountId& account_id,
+      const ScopeSet& scopes,
+      const OAuth2AccessTokenConsumer::TokenResponse& token_response);
+
   // Removes an access token for the given set of scopes from the cache.
   // Returns true if the entry was removed, otherwise false.
   bool RemoveCachedTokenResponse(const RequestParameters& client_scopes,