[3p-Conflicts] Fix accessibility issue in WebUI page

Make the list title a heading level 2

Bug: 820466
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ibc910786a94163da186671bc247670cb6d6a5d53
Reviewed-on: https://chromium-review.googlesource.com/964944Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Patrick Monette <pmonette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544725}

chrome/browser/resources/settings/incompatible_applications_page/incompatible_applications_page.html

@@ -36,7 +36,7 @@
         </div>
       </div>
       <div class="settings-box continuation">
-        <div class="secondary">[[listTitleText_]]</div>
+        <h2 class="secondary">[[listTitleText_]]</h2>
       </div>
       <div id="incompatible-applications-list" class="list-frame vertical-list">
         <template is="dom-repeat" items="[[applications_]]" as="application">