Updates SelectToSpeakEventHandler to change state when extension state changes.

This is part of a change to allow Select-to-Speak to work in tablet/touch only
mode.

This change allows the extension to tell the EventHandler that capturing should
being, allowing Select-to-Speak to start capturing touch events or mouse events
without the 'search' key having been clicked.

This change does not cause any behavior changes at this time, because there is
no current way to enter the SELECTING state without holding down the search key
first.

In a follow-up change, this pathway will be activated when a user will click
a button in the ash system shelf. That button is not yet hooked up. To see a
complete demo, see https://chromium-review.googlesource.com/c/chromium/src/+/1031550.

Bug: 753018
Change-Id: I3be60fa338ce32e2a99ce7e21d9d7cab503ac4e0
Reviewed-on: https://chromium-review.googlesource.com/1036534
Commit-Queue: Katie Dektar <[email protected]>
Reviewed-by: David Tseng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#555540}
4 files changed