[Nearby] Fix unwanted toggle animation.

If we launch the settings app by navigating to the Nearby Share subpage,
the "enabled" toggle can be seen animating from the off to the on state.
This is because prefs are not bound until after the page is visible.
Other elements also appear or update after the page loads, but this
toggle is especially noticeable because of the animation. This fix wraps
the toggle in a template so that it appears in the correct state after
prefs have been bound.

Fixed: 1158520
Change-Id: Ifbc753ca3faf6db65bba183621c861bc716c6746
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2602576Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Michael Hansen <hansenmichael@google.com>
Cr-Commit-Position: refs/heads/master@{#841163}

chrome/browser/resources/settings/chromeos/nearby_share_page/nearby_share_subpage.html

@@ -66,10 +66,16 @@
         [[getOnOffString_(prefs.nearby_sharing.enabled.value,
             '$i18nPolymer{deviceOn}', '$i18nPolymer{deviceOff}')]]
       </div>
-      <settings-toggle-button id="featureToggleButton" aria-describedby="onOff"
-          pref="{{prefs.nearby_sharing.enabled}}"
-          deep-link-focus-id$="[[Setting.kNearbyShareOnOff]]">
-      </settings-toggle-button>
+
+      <!-- Use a template to work around visual glitch where the toggle flips
+          on when the page first loads. -->
+      <template is="dom-if" if="[[prefs]]" restamp>
+        <settings-toggle-button id="featureToggleButton"
+            aria-describedby="onOff"
+            pref="{{prefs.nearby_sharing.enabled}}"
+            deep-link-focus-id$="[[Setting.kNearbyShareOnOff]]">
+        </settings-toggle-button>
+      </template>
     </div>
     <div class="settings-box two-line">
       <div class="start"