Closes #1340 - Add HistoryState to content state

[NotWoods]

---

Pull Request checklist

• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry or does not need one
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features

After merge

• Milestone: Make sure issues closed by this pull request are added to the milestone of the version currently in development.
• Breaking Changes: If this is a breaking change, please push a draft PR on Reference Browser to address the breaking issues.

[codecov]

Codecov Report

Merging #7024 into master will decrease coverage by 0.06%.
The diff coverage is 78.94%.

@@             Coverage Diff              @@
##             master    #7024      +/-   ##
============================================
- Coverage     77.16%   77.09%   -0.07%     
- Complexity     4632     4774     +142     
============================================
  Files           628      627       -1     
  Lines         22958    23475     +517     
  Branches       3342     3434      +92     
============================================
+ Hits          17716    18099     +383     
- Misses         3856     3951      +95     
- Partials       1386     1425      +39     

Impacted Files	Coverage Δ	Complexity Δ
...mozilla/components/concept/engine/EngineSession.kt	75.34% <0.00%> (-0.52%)	3.00 <0.00> (ø)
...a/components/concept/engine/history/HistoryItem.kt	33.33% <33.33%> (ø)	1.00 <1.00> (?)
...omponents/browser/session/engine/EngineObserver.kt	70.52% <75.00%> (+0.19%)	51.00 <1.00> (+1.00)
...a/components/browser/state/action/BrowserAction.kt	94.28% <100.00%> (+0.21%)	0.00 <0.00> (ø)
...nents/browser/state/reducer/ContentStateReducer.kt	81.08% <100.00%> (+3.30%)	26.00 <0.00> (+1.00)
...lla/components/browser/state/state/ContentState.kt	100.00% <100.00%> (ø)	19.00 <1.00> (+1.00)
...onents/browser/state/state/content/HistoryState.kt	100.00% <100.00%> (ø)	3.00 <3.00> (?)
...s/lib/push/firebase/AbstractFirebasePushService.kt	64.28% <0.00%> (-3.58%)	9.00% <0.00%> (ø%)
...ents/browser/icons/extension/IconMessageHandler.kt
.../components/browser/icons/extension/IconMessage.kt
... and 52 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9be6690...1a84e76. Read the comment docs.

[jonalmeida]

Did a quick review so far and this looks great! 🎉 Two things left and we can merge:

• Needs some tests for the EngineSessions and the EngineObserver.
• Update the issue ID in the comment.

[jonalmeida]

@NotWoods Nice! I think we're still missing tests for the GeckoEngineSession before we can merge, those should be straight-forward. 🙂

[jonalmeida]

bors r+

⚡

[bors]

Build succeeded:

• complete-push