Media Engagement: Fix bug when sorting by isHigh

Adds sort key handler for isHigh which will allow users to sort by
"isHigh" when using chrome://media-engagement.

BUG=792906

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I11db5ddf4843faca361eb9016535d582e6230fa5
Reviewed-on: https://chromium-review.googlesource.com/970584Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544693}

chrome/browser/resources/media/media_engagement.js

@@ -80,7 +80,7 @@ function compareTableItem(sortKey, a, b) {
   if (sortKey == 'visits' || sortKey == 'mediaPlaybacks' ||
       sortKey == 'lastMediaPlaybackTime' || sortKey == 'totalScore' ||
       sortKey == 'audiblePlaybacks' || sortKey == 'significantPlaybacks' ||
-      sortKey == 'highScoreChanges') {
+      sortKey == 'highScoreChanges' || sortKey == 'isHigh') {
     return val1 - val2;
   }