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ClosedTabCache is a desktop feature to instantly restore closed tabs.

To own ClosedTabCache, this CL adds a KeyedService called
ClosedTabCacheService and a BrowserContextKeyedServiceFactory,
ClosedTabCacheServiceFactory, to retrieve the service.

ClosedTabCache design doc:
https://docs.google.com/document/d/1SF230MYWgroe4WikDMn82ETd3-HFRzylKtIk0HZRaOU/edit?usp=sharing

BUG=1100946

Change-Id: I397aa3abbebd9098694b20b9385fe75a7958c484
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2564966Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Sreeja Kamishetty <sreejakshetty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832708}