GitLab

Instead of using SetInitializationThrottled(bool), initialization
throttling of a PolicyServiceImpl can only be activated at construction
time using CreateWithInitilizationThrottled and deactivated using
UnthrottleInitialization. This is clearer and guarantees that the state
of the service is consistent even when all PolicyProviders are already
initialized at construction time.

To be able to implement this properly, the meaning of the
|initialization_complete_| variable had to be changed - it can now be
true even when initialization is throttled. Initialization throttling
only means that observers are not notified yet.

Also add unit tests to test the behavior of initialization throttling.

Planned follow-up changes:
(*) Timeout to abort initialization throttling after a few seconds to
    protect against coding error.
(*) UMA stat to track initialization throttling time.

Bug: 982936, 1002066
Test: browser_test still pass, new components_unittests test

Change-Id: I32eb7fbac1746d25ab650ba0969e6cb7a1a22241
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1798324Reviewed-by: Lutz Justen <ljusten@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700174}