amend! [cr136][WIP] CalculateInsertionIndex dropped dragged_group

[cr136] `CalculateInsertionIndex` dropped `dragged_group`

Chromium changes:
https://chromium.googlesource.com/chromium/src/+/8430f0ead04470b637420ef2fe2f0ce3776a7339

commit 8430f0ead04470b637420ef2fe2f0ce3776a7339
Author: Taylor Bergquist <[email protected]>
Date:   Fri Mar 28 16:49:19 2025 -0700

    Update GetInsertionIndexForDraggedBounds to support mixed drags.

    Generalize TabDragContext::GetInsertionIndexForDraggedBounds to handle
    any mix of tabs and group headers. Inserting into a group is allowed if
    and only if there are no group headers being dragged. There is no
    behavior change for header drags nor for normal drags, because there
    isn't yet a way to start a mixed drag session.

    Bug: 406529549
    Change-Id: If7b0564d32f6e6946da1b5ff913a1d26d29f9f24
    Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6405742
    Reviewed-by: David Pennington <[email protected]>
    Commit-Queue: Taylor Bergquist <[email protected]>
    Cr-Commit-Position: refs/heads/main@{#1439783}

Author: emerick