Migrate addSelection from BrowserAccessiblity to AXPlatformNode

Bug: 703369
Change-Id: I749030e605eb30d3ee0785885d20c510e5f91f69
Reviewed-on: https://chromium-review.googlesource.com/659258
Commit-Queue: Doug Turner <dougt@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#502523}
3 files changed