GitLab

  * Move the cast AccessibilityManager into
    chromecast/browser/accessibility.
  * Only compile and create AccessibilityManager if extensions
    enabled.

Bug: none
Test: manual
Change-Id: I83c30b8259caa97093cdd48baafd26b2750d1da7
Reviewed-on: https://chromium-review.googlesource.com/1081234Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Kevin Schoedel <kpschoedel@chromium.org>
Reviewed-by: Alex Sakhartchouk <alexst@chromium.org>
Commit-Queue: Ryan Daum <rdaum@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564692}