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On a successful install/update, component_updater sends a dbus signal to
platform. This allows compnoent consumers to be notified instead of
retrying calling the Load API.

Include dbus in chrome/browser/DEPS

BUG=chromium:822902
TEST=sudo -u root dbus-monitor --system  "type='signal',sender='org.chromium.ComponentUpdaterService',interface='org.chromium.ComponentUpdaterService'"

Change-Id: Ie913658329e6eb0cf0deb030fc772ec03fdbd8ea
Reviewed-on: https://chromium-review.googlesource.com/984600
Commit-Queue: Xiaochu Liu <xiaochu@chromium.org>
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554921}