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This is just a basic class that can convert from a DOM selection to an AX range and vice versa. It can also perform a selection on the AX range.
This class doesn't still handle any of the many corner cases that I will be looking at next, cases that will be covered by tests.
R=dmazzoni@chromium.org

Bug: 
Change-Id: I7c98617e8ef3b8bcca8cfc0d2e5518f2da771063
Reviewed-on: https://chromium-review.googlesource.com/678016
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542619}