Disabling "Show Whitespace changes" takes minutes to take affect

Summary

When a "large" merge request diff is viewed (70 files, 9000 additions, 9000 deletions) and the "Show Whitespace Changes" option is disabled, it takes the page minutes to update causing Chrome to give an unresponsive page notification.

When you copy the URL and disable white space by adding the ws=1 parameter in the URL, the page renders quickly as expected.

Steps to reproduce

1. View a diff with many files and changes (70 files, 9000 additions, 9000 deletions)
2. Disable "Show whitespace changes"
3. The page will take minutes to render and chrome will deem it unresponsive

Example Project

We are using Gitlab Starter 12.0

What is the current bug behavior?

Disabling show whitespace changes via the checkbox takes on the order of minutes while setting the URL parameter and refreshing takes seconds.

What is the expected correct behavior?

Disabling show whitespace changes via the checkbox should take on the order of seconds similar to setting it via URL parameter.

Relevant logs and/or screenshots

N/A

Output of checks

N/A

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:         Ubuntu 16.04 
Proxy:          no
Current User:   git 
Using RVM:      no
Ruby Version:   2.6.3p62
Gem Version:    2.7.9
Bundler Version:1.17.3
Rake Version:   12.3.2
Redis Version:  3.2.12
Git Version:    2.21.0
Sidekiq Version:5.2.7
Go Version:     unknown
GitLab information
Version:        12.0.3-ee
Revision:       1b1872f9d93
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     PostgreSQL
DB Version:     10.7
URL:            ***
HTTP Clone URL: ***
SSH Clone URL: ***
Elasticsearch:  no
Geo:            no
Using LDAP:     yes
Using Omniauth: yes
Omniauth Providers:
GitLab Shell
Version:        9.3.0
Repository storage paths:

• default: /var/opt/gitlab/git-data/repositories GitLab Shell path: /opt/gitlab/embedded/service/gitlab-shell Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab subtasks ...
Checking GitLab Shell ...
GitLab Shell: ... GitLab Shell version >= 9.3.0 ? ... OK (9.3.0)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Gitaly ...
Gitaly: ... default ... OK
Checking Gitaly ... Finished
Checking Sidekiq ...
Sidekiq: ... Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Checking Incoming Email ...
Incoming Email: ... Reply by email is disabled in config/gitlab.yml
Checking Incoming Email ... Finished
Checking LDAP ...
LDAP: ... Server: ldapmain
Checking LDAP ... Finished
Checking GitLab App ...
Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... 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: ...
3/1 ... yes
10/6 ... yes
12/7 ... yes
11/9 ... yes
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188/295 ... yes
188/296 ... yes
82/297 ... yes
59/298 ... yes
188/300 ... yes
188/301 ... yes
175/302 ... yes
206/303 ... yes
12/304 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.5.3 ? ... yes (2.6.3)
Git version >= 2.21.0 ? ... yes (2.21.0)
Git user has default SSH configuration? ... yes
Active users: ... ***
Elasticsearch version 5.6 - 6.x? ... skipped (elasticsearch is disabled)
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished

Possible fixes

/label ~bug