GitLab

After landing of https://codereview.chromium.org/651593002,
the inheritance relationship between RendererAccessibility and
RendererAccessibiltiyComplete is not necessary anymore.
So we can make them one class.

BUG=417758

Review URL: https://codereview.chromium.org/688173002

Cr-Commit-Position: refs/heads/master@{#302197}