Moving tabs sometimes doesn't respect the correct position

[bbondy]

Test plan

See below

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• Did you search for similar issues before submitting this one?
  yes

• Describe the issue you encountered:
  After closing some tabs in a window, sometimes dropping a tab at a specific spot will move the tab to a different spot. Often 2 to the left.

• Platform (Win7, 8, 10? macOS? Linux distro?):
  macOS, but probably all

• Brave Version (revision SHA):
  0.18.29

• Steps to reproduce:

  1. Open 7 tabs
  2. Close the middle 2
  3. Move the first tab to another position

• Actual result:
  Sometimes the drop position isn't consistent with where the tab gets moved to

• Expected result:
  The tab should be moved where it was dropped

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes but it seems harder.

• Is this an issue in the currently released version?
  Yes

• Can this issue be consistently reproduced?
  Not 100% but if you play with it for a couple minutes you'll get it, it seems somewhat related to tab close.