Add aleventhal as owner for blink accessibility

Bug: None
Change-Id: Ic1d11908700ad0460df817cc368204e9de2d4f12
Reviewed-on: https://chromium-review.googlesource.com/995616
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548151}

third_party/WebKit/Source/modules/accessibility/OWNERS

 aboxhall@chromium.org
+aleventhal@chromium.org
 dmazzoni@chromium.org
 nektar@chromium.org