[Security] Mixed content is no longer being auto-upgraded

[LaurenWags]

Description

With C83 mixed content stopped being auto-upgraded (implemented with #4381).

Steps to Reproduce

1. Open https://mixed.badssl.com
2. Click the padlock icon and make sure it's marked as secure.

Actual result:

Expected result:

Should be as it was in 1.9.x (w/ C81):

Reproduces how often:

easily

Brave version (brave://version info)

Brave	1.10.86 Chromium: 83.0.4103.61 (Official Build) (64-bit)
Revision	94f915a8d7c408b09cc7352161ad592299f384d2-refs/branch-heads/4103@{#561}
OS	macOS Version 10.14.6 (Build 18G3020)

Version/Channel Information:

• Can you reproduce this issue with the current release? 1.9.x no, 1.10.x (w/ C83) yes
• Can you reproduce this issue with the beta channel? yes
• Can you reproduce this issue with the dev channel? yes
• Can you reproduce this issue with the nightly channel? yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information:

cc @rebron @bsclifton @fmarier @brave/legacy_qa

[diracdeltas]

This should be automatically fixed by https://chromium-review.googlesource.com/c/chromium/src/+/2454853, which is in cr88. I cherry-picked part of that change into cr87 and verified that it fixes the issue.

[LaurenWags]

Verified passed with

Brave | 1.20.84 Chromium: 88.0.4324.96 (Official Build) dev (x86_64)
-- | --
Revision | 68dba2d8a0b149a1d3afac56fa74648032bcf46b-refs/branch-heads/4324@{#1784}
OS | macOS Version 10.15.7 (Build 19H15)

Verified STR from description.

---

Verification passed on

Brave | 1.20.84 Chromium: 88.0.4324.96 (Official Build) dev (64-bit)
-- | --
Revision | 68dba2d8a0b149a1d3afac56fa74648032bcf46b-refs/branch-heads/4324@{#1784}
OS | Windows 10 OS Version 2004 (Build 19041.746)

• Verified the STR from the description
  

---

Verification passed on

Brave	1.20.86 Chromium: 88.0.4324.96 (Official Build) dev (64-bit)
Revision	68dba2d8a0b149a1d3afac56fa74648032bcf46b-refs/branch-heads/4324@{#1784}
OS	Ubuntu 18.04 LTS

Verified STR from description.