Privacy Stats not shown on navigation back

[chrmod]

In case when page is loaded from in memory cache - for instance back/forward navigation, there are no requests being block so Content Blocker does not register any Ads/Trackers. Even though technically it is not a bug, it appear as one to users as expectation is to always see how many trackers were blocked.

Potential fix could involve maintaing small in memory cache for Content Blocker stats (per tab), which will be revivied on back/forward navigation.

Challange is to figure out when it should be cleared to prevent memory leaks. But maybe it is not a problems as those stats are very light.