Only count markers that are part of the selected range when hovering a marker in the marker chart.

[fqueze]

Fixes a bug in the implementation of #4892.

Steps to reproduce:

• Load this example profile: https://share.firefox.dev/3wMQqtN
• Hover a marker and see the marker count
• Change the preview selection
• See that less markers are drawn
• Hover a marker. Notice the marker count is still the same as before; it should be lower.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.46%. Comparing base (ffe2b6a) to head (1a18805).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5004   +/-   ##
=======================================
  Coverage   88.46%   88.46%           
=======================================
  Files         304      304           
  Lines       27317    27329   +12     
  Branches     7377     7378    +1     
=======================================
+ Hits        24165    24177   +12     
  Misses       2930     2930           
  Partials      222      222           

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[julienw]

I'm not super happy about this duplication, but let's do that...
I wanted to ask you about improving the tests, but I see there's no existing test for the marker chart when a preview selection is active 😱. If you want to add one I'd be glad but I won't make you do one.

[fqueze]

Thanks for the review!

I'm not super happy about this duplication, but let's do that...

I'm not super happy about the duplication either. I initially wanted to make a shared method returning timeAtViewportLeft and timeAtViewportRightPlusMargin, but then I realized some of the intermediary variables are used for the other caller, so I wouldn't actually win much.