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A web notification with the inline reply actions is already implemented
on Android and Windows 10 native notifications.
In order to support the feature on Chrome OS, we have to implement it
in the views framework notification implementation.

This CL adds the non user interface part of the notification inline
reply support.

TEST=manual
BUG=599859,773586

Change-Id: Ib6079f8dadd5e154e68a5c32b5c99df2fb100499
Reviewed-on: https://chromium-review.googlesource.com/756184Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516969}