Check current screen status before calling updateScreenSize on arc screen

Bug: 775687
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I03f030f0e6210b907d5c890f7b8bbf7b1cce9e8e
Reviewed-on: https://chromium-review.googlesource.com/724879Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509976}

chrome/browser/resources/chromeos/login/screen_arc_terms_of_service.js

@@ -110,7 +110,8 @@ login.createScreen('ArcTermsOfServiceScreen', 'arc-tos', function() {
       };
 
       // Update the screen size after setup layout.
-      Oobe.getInstance().updateScreenSize(this);
+      if (Oobe.getInstance().currentScreen === this)
+        Oobe.getInstance().updateScreenSize(this);
     },
 
     /**