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 Test: manually click (with ChromeVox using Search+Space) ARC++ notification; verify app opens.
Bug: 786981

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I6809ff0371e5315e0fe6aaf01e9c567215c77fc4
Reviewed-on: https://chromium-review.googlesource.com/783669
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519532}