Close UnifiedSystemTray on settings button click.

We should explicitly close UnifiedSystemTray when the settings button is
clicked.

TEST=manual
BUG=853610

Change-Id: I029396b33a3bdde0d64e5b89a01c53ba38e72f96
Reviewed-on: https://chromium-review.googlesource.com/1103436Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568324}

ash/system/unified/unified_system_tray_controller.cc

@@ -120,6 +120,7 @@ void UnifiedSystemTrayController::HandleLockAction() {
 void UnifiedSystemTrayController::HandleSettingsAction() {
   Shell::Get()->metrics()->RecordUserMetricsAction(UMA_TRAY_SETTINGS);
   Shell::Get()->system_tray_controller()->ShowSettings();
+  CloseBubble();
 }
 
 void UnifiedSystemTrayController::HandlePowerAction() {