Elements not blocked by selector when tab loaded in background

[wooque]

Description

Elements that are blocked by selector are blocked if tab is loaded in current tab, but not if tab is loaded in background.

Steps to Reproduce

1. Block any element via selector on any page
2. Bookmark page
3. Open that bookmark with 'Open link in new tab'

[more detailed STR in https://github.com/brave/brave-core/pull/3121]

Actual result:

Element not blocked when tab opened in background

Expected result:

Element blocked

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Brave	0.66.99 Chromium: 75.0.3770.100 (Official Build)unknown (64-bit)
Revision	cd0b15c8b6a4e70c44e27f35c37a4029bad3e3b0-refs/branch-heads/3770@{#1033}
OS	Linux

Version/Channel Information:

• Can you reproduce this issue with the current release? 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? No
• Does the issue resolve itself when disabling Brave Rewards? No
• Is the issue reproducible on the latest version of Chrome? /

[btlechowski]

Verification passed on

Brave	0.69.129 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Ubuntu 18.04 LTS

Reproduced the issue in 0.68.141.
Verified test plan from brave/brave-core#3121

Verification passed on

Brave	0.69.129 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• The original issue is reproduced in 0.68.141
• Verified the test plan from fix cosmetic filtering brave-core#3121

Verified passed with

Brave	0.69.129 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	macOS Version 10.13.6 (Build 17G5019)

• Verified the test plan from fix cosmetic filtering brave-core#3121