Reauth causes a MergeSession, so the cookie jar gets re-authed too.

chrome/browser/ui/webui/signin/inline_login_handler_impl.cc

Index: chrome/browser/ui/webui/signin/inline_login_handler_impl.cc
diff --git a/chrome/browser/ui/webui/signin/inline_login_handler_impl.cc b/chrome/browser/ui/webui/signin/inline_login_handler_impl.cc
index d9ed6882a2324458d01520760ef12797b0cd1eb0..632dd5f7302c4e018ac7c8088510e704e9144bd3 100644
--- a/chrome/browser/ui/webui/signin/inline_login_handler_impl.cc
+++ b/chrome/browser/ui/webui/signin/inline_login_handler_impl.cc
@@ -48,7 +48,8 @@
 
 namespace {
 
-class InlineSigninHelper : public GaiaAuthConsumer {
+class InlineSigninHelper : public GaiaAuthConsumer,
+                           public MergeSessionHelper::Observer {
  public:
   InlineSigninHelper(
       base::WeakPtr<InlineLoginHandlerImpl> handler,
@@ -69,6 +70,10 @@ class InlineSigninHelper : public GaiaAuthConsumer {
   void OnClientOAuthFailure(const GoogleServiceAuthError& error)
       override;
 
+  // Overridden from MergeSessionHelper::Observer.
+  void MergeSessionCompleted(const std::string& account_id,
+                             const GoogleServiceAuthError& error) override;
+
   GaiaAuthFetcher gaia_auth_fetcher_;
   base::WeakPtr<InlineLoginHandlerImpl> handler_;
   Profile* profile_;
@@ -79,6 +84,8 @@ class InlineSigninHelper : public GaiaAuthConsumer {
   std::string session_index_;
   bool choose_what_to_sync_;
   bool confirm_untrusted_signin_;
+  // Helper to merge signed in account into the content area.
+  scoped_ptr<MergeSessionHelper> merge_session_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(InlineSigninHelper);
 };
@@ -145,8 +152,9 @@ void InlineSigninHelper::OnClientOAuthSuccess(const ClientOAuthResult& result) {
 
   if (source == signin_metrics::SOURCE_AVATAR_BUBBLE_ADD_ACCOUNT ||
       source == signin_metrics::SOURCE_REAUTH) {
-    ProfileOAuth2TokenServiceFactory::GetForProfile(profile_)->
-        UpdateCredentials(account_id, result.refresh_token);
+    ProfileOAuth2TokenService* token_service =
+        ProfileOAuth2TokenServiceFactory::GetForProfile(profile_);
+    token_service->UpdateCredentials(account_id, result.refresh_token);
 
     if (signin::IsAutoCloseEnabledInURL(current_url_)) {
       // Close the gaia sign in tab via a task to make sure we aren't in the
@@ -157,6 +165,17 @@ void InlineSigninHelper::OnClientOAuthSuccess(const ClientOAuthResult& result) {
           handler_,
           signin::ShouldShowAccountManagement(current_url_)));
     }
+
+    SigninClient* signin_client =
+        ChromeSigninClientFactory::GetForProfile(profile_);
+    if (signin_client->ShouldMergeSigninCredentialsIntoCookieJar()) {
+        merge_session_helper_.reset(new MergeSessionHelper(
+            token_service, GaiaConstants::kChromeSource,
+            signin_client->GetURLRequestContext(), NULL));
+        merge_session_helper_->LogIn(account_id);
+    } else {
+      base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
+    }

[Roger Tawa OOO till Jul 10th, 2015/02/12 14:54:38]

As discussed offline, it would be better to refactor the signin manager code and
expose a method to perform the merge session instead of using a second instance
of merge_session_helper_ here.

[Mike Lerman, 2015/02/13 19:17:06]

Done.

   } else {
     ProfileSyncService* sync_service =
         ProfileSyncServiceFactory::GetForProfile(profile_);
@@ -214,9 +233,8 @@ void InlineSigninHelper::OnClientOAuthSuccess(const ClientOAuthResult& result) {
           signin::GetNextPageURLForPromoURL(current_url_),
           base::Bind(&InlineLoginHandlerImpl::SyncStarterCallback, handler_));
     }
+    base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
   }
-
-  base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 }
 
 void InlineSigninHelper::OnClientOAuthFailure(
@@ -231,6 +249,12 @@ void InlineSigninHelper::OnClientOAuthFailure(
   base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 }
 
+void InlineSigninHelper::MergeSessionCompleted(
+    const std::string& account_id,
+    const GoogleServiceAuthError& error) {
+  base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
+}
+
 }  // namespace
 
 InlineLoginHandlerImpl::InlineLoginHandlerImpl()