Ignore ATS::Observer::OnAccountUpdateFailed from AccountManagerUIHandler

Since the patch in CL1406976 for crbug.com/833797 landed (see [1]), there
is not any need to monitor this event since AccountManagerUIHandler is no
longer taking accounts out of the UI while data is being fetched, and so
there is no need to do this extra effort to make sure that such accounts
were added back once that fetch was complete.

Additionally, removing this method now paves the way to migrate away from
AccountTrackerService APIs entirely from AccountManagerUIHandler, and use
IdentityManager's APIs instead, so let's do it now as a precursor CL.

[1] https://crrev.com/c/1406976

Bug: 922785
Change-Id: I068e89eb7fa7774c3be0f9bf67e02a0b8dfb642d
Reviewed-on: https://chromium-review.googlesource.com/c/1437175Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#626231}

chrome/browser/ui/webui/settings/chromeos/account_manager_handler.cc

@@ -247,14 +247,6 @@ void AccountManagerUIHandler::OnAccountUpdated(const AccountInfo& info) {
   RefreshUI();
 }
 
-void AccountManagerUIHandler::OnAccountUpdateFailed(
-    const std::string& account_id) {
-  // An account fetch failed for |account_id|, but we must display the account
-  // anyways (if it was not being displayed already) so that users do not think
-  // that their account has suddenly disappeared.
-  RefreshUI();
-}
-
 void AccountManagerUIHandler::OnAccountRemoved(const AccountInfo& account_key) {
 }
 

chrome/browser/ui/webui/settings/chromeos/account_manager_handler.h

@@ -44,7 +44,6 @@ class AccountManagerUIHandler : public ::settings::SettingsPageUIHandler,
 
   // |AccountTrackerService::Observer| overrides.
   void OnAccountUpdated(const AccountInfo& info) override;
-  void OnAccountUpdateFailed(const std::string& account_id) override;
   void OnAccountRemoved(const AccountInfo& account_key) override;
 
  private: