This CL splits a cross platform subset of
ChromeComponentUpdaterConfigurator into
//components/component_updater/configurator_impl
That way the code can be shared on iOS.

This CL also provides a iOS implementation of the configurator in
//ios/chrome.

BUG=517890

Review URL: https://codereview.chromium.org/1281913002

Cr-Commit-Position: refs/heads/master@{#344173}