[Desktop] Add diagnostics about loading the refresh tokens.

components/signin/core/browser/about_signin_internals.h

Index: components/signin/core/browser/about_signin_internals.h
diff --git a/components/signin/core/browser/about_signin_internals.h b/components/signin/core/browser/about_signin_internals.h
index 3caeb6ebd3e34ae4a6432da55a34527f87e691ab..8e42feab40957090fe2a07f698602ddf633ec8a8 100644
--- a/components/signin/core/browser/about_signin_internals.h
+++ b/components/signin/core/browser/about_signin_internals.h
@@ -37,6 +37,7 @@ using TimedSigninStatusValue = std::pair<std::string, std::string>;
 class AboutSigninInternals
     : public KeyedService,
       public signin_internals_util::SigninDiagnosticsObserver,
+      public OAuth2TokenService::Observer,
       public OAuth2TokenService::DiagnosticsObserver,
       public GaiaCookieManagerService::Observer,
       SigninManagerBase::Observer,
@@ -184,6 +185,9 @@ class AboutSigninInternals
   void OnTokenRemoved(const std::string& account_id,
                       const OAuth2TokenService::ScopeSet& scopes) override;
 
+  // OAuth2TokenServiceDelegate::Observer implementations.
+  void OnRefreshTokensLoaded() override;
+
   // SigninManagerBase::Observer implementations.
   void GoogleSigninFailed(const GoogleServiceAuthError& error) override;
   void GoogleSigninSucceeded(const std::string& account_id,