Cookie controls toggle voice-over

To address
https://bugs.chromium.org/p/chromium/issues/detail?id=1005788#c41;
allow screen reader to read out a text associated to cookie controls
toggle.

Bug: 1017143
Change-Id: I9031d3f82bcda44b0e8b6fd59c8e9b6a43dfc930
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1876387Reviewed-by: Dan Beam <dbeam@chromium.org>
Commit-Queue: Huanzhong Huang <huanzhong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708702}

chrome/browser/resources/ntp4/incognito_tab.html

@@ -36,6 +36,7 @@ document.write('<link id="incognitothemecss" rel="stylesheet" ' +
       $i18n{cookieControlsDescription}
     </div>
     <cr-toggle id="cookie-controls-toggle"
+               aria-label="$i18n{cookieControlsTitle}"
                $i18n{cookieControlsToggleChecked} dark></cr-toggle>
   </div>
   <a class="learn-more-button" href="$i18n{learnMoreLink}">$i18n{learnMore}</a>