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This CL introduces new class for invalidation Topics, it's temporary
called TopicData, but will be renamed to Topic once legacy Topic alias
usages will be removed.

TopicData contains topic name and a boolean to identify whether topic
is public. It would allow us to simplify external API and clean up
internal usages of Topics - having TopicMetadata and Topics in some
places and Topic names and TopicSet in other places is confusing.

This CL modifies
InvalidatorRegistrarWithMemory::UpdateRegisteredTopics() to use the new
class. Internal usages in InvalidatorRegistrarWithMemory also updated,
but a bunch of methods exposes old Topics, because they are used
outside components/invalidation and it's better to update them on later
stages.

There is one potential behavioral change in case of existing bug in the
code: topics subscriptions were stored in prefs without |is_public|
field, before migration was introduced in
https://cr-rev.appspot.com/c/1570963. This migration assumes that all
previously stored topics are private and likely happened when there was
no public topics in launched projects. If this statement isn't
accurate, then there is a behavioral change:
Before: public topic subscription loaded from legacy prefs, the code
assumes it's a private topic until the same topic is passed into
UpdateInterestedTopics().
After: buggy version of public topic remains in "interesting" state,
once UpdateInterestedTopics() is called with correct TopicData there
are two version of this Topic (one is private (buggy) and one is public
(correct)).
It happens because |is_public| become a part of Topic identifier.

Bug: 1029698
Change-Id: I8febb82aa7f0294ccb4198467f5bd0f56bbd5798
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2091351
Commit-Queue: Maksim Moskvitin <mmoskvitin@google.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749629}