feedback: Hide minimize button on login screen.

"Minimize" doesn't function appropriately on the login screen, so don't
show it there.

BUG=chromium:1129631
TEST=deployed to a juniper device, verified minimize button was absent\
    on login screen and present and functional when user logged in

Fixed: chromium:1129631
Change-Id: Ie782407137398927179e4685b3de04e11acb27d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2419386
Auto-Submit: Miriam Zimmerman <mutexlox@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808647}

chrome/browser/resources/feedback/js/feedback.js

@@ -439,11 +439,13 @@ function initialize() {
         $('attach-file').hidden = true;
       }
 
-      // No URL and file attachment for login screen feedback.
+      // No URL, file attachment, or window minimizing for login screen
+      // feedback.
       if (feedbackInfo.flow == chrome.feedbackPrivate.FeedbackFlow.LOGIN) {
         $('page-url').hidden = true;
         $('attach-file-container').hidden = true;
         $('attach-file-note').hidden = true;
+        $('minimize-button').hidden = true;
       }
 
       // <if expr="chromeos">