split view tabs width is not equally distributed when pdf/word file added to split view

[GeetaSarvadnya]

Description

Found while testing #36986
split view tabs width is not equally distributed when pdf/word file added to split view

Steps to reproduce

1. Clean profile 1.76.69
2. Open https://www.pdf995.com/samples/pdf.pdf or open any pdf via local file system
3. Create a split view
4. split view tab width between pdf and NTP tab isn't equal

Actual result

split view tabs width is not equally distributed when pdf/word file added to split view

Screen.Recording.2025-02-28.at.3.02.04.PM.mov

Expected result

split view tabs width should be equally distributed when pdf/word file added to split view

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave	1.76.69 Chromium: 134.0.6998.24 (Official Build) beta (arm64)
Revision	55ecc732897c3be718a5d828607782d3c54a2271
OS	macOS Version 15.3.1 (Build 24D70)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

• with Brave Shields disabled
• with Brave Rewards disabled
• in the latest version of Chrome

Miscellaneous information

cc: @rebron @brave/qa-team @simonhong