Tabs characters in code seems broken in code views & diffs in GitLab CE v8.1

Our code base uses tabs characters (0x09, \t) for indentation with a convention of a width of 4 spaces.

Since the upgrade to GitLab v8.1, Chromium (Chrome) does not render the tabs properly any more.

Chromium used to use a width of 8 for the tabs characters but now there is no more indentation visible at all.

Here are two screenshots taken under Chromium and Firefox showing the problem under Chromium. The same commit (of a Python 2.7 class) was rendered in both browsers. Firefox "properly" indent the code (though using 8 spaces, see #2479 (moved)) while Chromium does not indent the code at all.

Chromium

45.0.2454.101 Ubuntu 14.04 (64-bit)

Firefox

41.0.2

This is a regression since GitLab 8.0 was behaving as expected, both in Chromium and Firefox (tabs rendered with width of 8 spaces). Problem occurs with GitLab-CE 8.1.0, 8.1.1 and 8.1.2 (8c8af7b6).

What is weird is that I cannot use the workaround I found in #2479 (moved) to set a tab-size anymore.

sudo -u git -H /opt/gitlab/bin/gitlab-rake gitlab:check RAILS_ENV=production SANITIZE=true
Checking GitLab Shell ...

GitLab Shell version >= 2.6.5 ? ... OK (2.6.5)
Repo base directory exists? ... yes
Repo base directory is a symlink? ... no
Repo base owned by git:git? ... yes
Repo base access is drwxrws---? ... yes
hooks directories in repos are links: ... 
2/1 ... ok
2/5 ... ok
2/6 ... ok
2/7 ... ok
2/8 ... ok
2/11 ... ok
2/12 ... ok
2/13 ... ok
2/14 ... ok
2/15 ... ok
2/16 ... ok
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Check directories and files: 
	/var/opt/gitlab/git-data/repositories: OK
	/var/opt/gitlab/.ssh/authorized_keys: OK
Test redis-cli executable: redis-cli 2.8.21
Send ping to redis server: PONG
gitlab-shell self-check successful

Checking GitLab Shell ... Finished

Checking Sidekiq ...

Running? ... yes
Number of Sidekiq processes ... 1

Checking Sidekiq ... Finished

Checking Reply by email ...

Reply by email is disabled in config/gitlab.yml

Checking Reply by email ... Finished

Checking LDAP ...

LDAP is disabled in config/gitlab.yml

Checking LDAP ... Finished

Checking GitLab ...

Git configured with autocrlf=input? ... yes
Database config exists? ... yes
Database is SQLite ... no
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config outdated? ... no
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory setup correctly? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
projects have namespace: ... 
2/1 ... yes
2/5 ... yes
2/6 ... yes
2/7 ... yes
2/8 ... yes
2/11 ... yes
2/12 ... yes
2/13 ... yes
2/14 ... yes
2/15 ... yes
2/16 ... yes
Redis version >= 2.4.0? ... yes
Ruby version >= 2.1.0 ? ... yes (2.1.7)
Your git bin path is "/opt/gitlab/embedded/bin/git"
Git version >= 1.7.10 ? ... yes (2.6.1)
Active users: 3

Checking GitLab ... Finished

 sudo -u git -H /opt/gitlab/bin/gitlab-rake gitlab:env:info RAILS_ENV=production

System information
System:		Ubuntu 14.04
Current User:	git
Using RVM:	no
Ruby Version:	2.1.7p400
Gem Version:	2.2.5
Bundler Version:1.10.6
Rake Version:	10.4.2
Sidekiq Version:3.3.0

GitLab information
Version:	8.1.2
Revision:	8c8af7b
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
URL:		http://***.***.***.***
HTTP Clone URL:	http://***.***.***.***/some-group/some-project.git
SSH Clone URL:	git@***.***.***.***:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	no

GitLab Shell
Version:	2.6.5
Repositories:	/var/opt/gitlab/git-data/repositories
Hooks:		/opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:		/opt/gitlab/embedded/bin/git