The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4c520183cb626cf66bbfad7c58a7e3e128a8accc

commit 4c520183cb626cf66bbfad7c58a7e3e128a8accc
Author: sorin <sorin@chromium.org>
Date: Fri Aug 19 17:27:44 2016

Provide a callback for Component Updater OnDemand calls.

The idea here is that there is no good way for a client to know
when a subsequent OnDemand call can be issued without getting
an Error::ERROR_UPDATE_IN_PROGRESS. This issue showed up when writing a
browser test for an unrelated component updater feature.

This change is mostly mechanical, especially for the existing users
of the OnDemand interface. All existing call sites pass a null callback
as an argument, therefore no new code paths are introduced with this change.

BUG= 639180 

Review-Url: https://codereview.chromium.org/2261533003
Cr-Commit-Position: refs/heads/master@{#413178}

[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/chrome/browser/component_updater/supervised_user_whitelist_installer.cc
[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/chrome/browser/component_updater/supervised_user_whitelist_installer_unittest.cc
[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/chrome/browser/plugins/plugin_observer.cc
[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/chrome/browser/ui/webui/components_ui.cc
[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/components/component_updater/component_updater_service.cc
[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/components/component_updater/component_updater_service.h
[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/components/component_updater/component_updater_service_internal.h
[modify] https://crrev.com/4c520183cb626cf66bbfad7c58a7e3e128a8accc/components/component_updater/component_updater_service_unittest.cc