Settings WebUI: Fix runtime errors when closing security keys dialogs.

Bug: 948237
Change-Id: I9138ee2e8e49cdb2ea5a19cd78ccde5e631d9b5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1548234
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Adam Langley <agl@chromium.org>
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646497}

chrome/browser/resources/settings/privacy_page/security_keys_subpage.html

@@ -13,11 +13,13 @@
     <style include="settings-shared"></style>
 
     <cr-link-row
+      id="setPINButton"
       class="hr"
       label="$i18n{securityKeysSetPIN}"
       sub-label="$i18n{securityKeysSetPINDesc}"
       on-click="onSetPIN_"></cr-link-row>
     <cr-link-row
+      id="resetButton"
       class="hr"
       label="$i18n{securityKeysReset}"
       sub-label="$i18n{securityKeysResetDesc}"