Move Auto Open Downloads block into neon-animatable tag

This change fixes a https://crbug.com/851937 where users are unable to
clear auto-opening downloads settings.

Bug: chromium:851937
Test: verified manually
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I263ef9497a8a9b298a3514404fc3f31a61393687
Reviewed-on: https://chromium-review.googlesource.com/1099693Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567299}

chrome/browser/resources/settings/downloads_page/downloads_page.html

@@ -51,8 +51,6 @@
           label="$i18n{disconnectGoogleDriveAccount}"
           hidden="[[!pageVisibility.googleDrive]]">
       </settings-toggle-button>
-</if>
-<if expr="chromeos">
       <template is="dom-if" if="[[enableSmbSettings_]]">
         <div id="smbShares" class="settings-box"
             on-click="onTapSmbShares_" actionable>
@@ -63,7 +61,6 @@
         </div>
       </template>
 </if>
-</neon-animatable>
       <template is="dom-if" if="[[autoOpenDownloads_]]" restamp>
         <div class="settings-box">
           <div class="start">
@@ -76,6 +73,8 @@
           </paper-button>
         </div>
       </template>
+    </neon-animatable>
+
 <if expr="chromeos">
     <template is="dom-if" route-path="/smbShares">
       <settings-subpage