Fix white space on pages left by blocked ads in certain cases

[Brave-Matt]

Description

Some sites with ads blocked will leave white space on the page where the ad was blocked. In some cases, whitespace seems to be added to the page as well.

Note that this may be related to region as most of the users reporting seem to be outside the US.

Steps to Reproduce

1. Visit bitcoinbazis.hu
2. Ensure Shields are set to default or at least that Ads are blocked
   [Detailed STR on PR]

Actual result:

Expected result:

Reproduces how often:

Easily

Version/Channel Information:

Occurs on all channels

• Can you reproduce this issue with the current release? ✅
• Can you reproduce this issue with the beta channel? ✅
• Can you reproduce this issue with the dev channel? ✅
• Can you reproduce this issue with the nightly channel? ✅

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
  Yes -- setting Ads control to Allow ads/tracking also renders page correctly.
• Does the issue resolve itself when disabling Brave Rewards?
  No
• Is the issue reproducible on the latest version of Chrome?
  No

Miscellaneous Information:

User reports (more to come):
https://community.brave.com/t/this-is-getting-really-annoying/55928
https://community.brave.com/t/page-rendering-issue/58045

[petemill]

Fixed via brave/brave-core#3121

[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

Verified bitcoinbazis.hu

The issue still reproduces on https://www.dia.net.au/. Logged #6190.

Verification PASSED on macOS 10.14.6 x64 using the following build:

Brave	0.69.129 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	macOS Version 10.14.6 (Build 18G95)

• Verified test case outlined under fix cosmetic filtering brave-core#3121
• ensured bitcoinbazis.hu was loading correctly
• reproduced the same issue @btlechowski mentioned re: https://www.dia.net.au

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)

• Verified test case outlined under fix cosmetic filtering brave-core#3121
• ensured bitcoinbazis.hu was loading correctly
• reproduced the same issue @btlechowski mentioned re: https://www.dia.net.au