Rename AXHostDelegate to AXActionHandler, part 2

Rename the files. The class was renamed in a separate CL to preserve
git history across the rename.

TBR=dtseng@chromium.org, halliwell@chromium.org, kenrb@chromium.org

Bug: none
Test: compiles
Change-Id: Ib4d41840ab9c6146e0d6fcc34959c36153df8b32
Reviewed-on: https://chromium-review.googlesource.com/c/1379249
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616914}
12 files changed