Fixes #1970 - Guards the close listener

[boek]

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

[pocmo]

with test and changelog 💯

[jonalmeida]

Heh, I was just fixing this but I think your solution works as well.

fun onBackPressed() = sessionManager.runWithSession(sessionId) {
    closeListener.invoke()
    remove(it)
    true
}

[pocmo]

It looks like this broke one test though:

mozilla.components.feature.customtabs.CustomTabsToolbarFeatureTest > onBackPressed removes session FAILED
    java.lang.AssertionError at CustomTabsToolbarFeatureTest.kt:323

(And there's a changelog conflict now :()

[codecov]

Codecov Report

Merging #1972 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #1972      +/-   ##
============================================
- Coverage      84.2%   84.19%   -0.01%     
+ Complexity     2081     2079       -2     
============================================
  Files           261      261              
  Lines          8642     8638       -4     
  Branches       1294     1294              
============================================
- Hits           7277     7273       -4     
  Misses          826      826              
  Partials        539      539

Impacted Files	Coverage Δ	Complexity Δ
...nts/feature/customtabs/CustomTabsToolbarFeature.kt	93.22% <100%> (ø)	17 <0> (ø)	⬇️
...illa/components/service/glean/BooleanMetricType.kt	100% <0%> (ø)	7% <0%> (-2%)	⬇️

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