Public content settings are not inherited by private window

[bsclifton]

Description

Public content settings are not inherited by private window. I believe these values are initialized with https://github.com/brave/brave-core/blob/master/components/content_settings/core/browser/brave_host_content_settings_map.cc, but because the extension has it's incognito property set to split, it may not be able to directly access the regular scoped content_settings. More investigation is needed

Problem was exposed when fixing #1198

Per #1721 - if no public settings exist for a given site, private window should inherit the global setting

Steps to Reproduce

Private window inheriting from existing public content setting

1. Open a new regular tab and visit https://dailymail.co.uk
2. Using shields icon, disable shields
3. Open a new private window
4. Visit https://dailymail.co.uk in that private window

Private window inheriting from global settings

1. Change your global settings to be adblock off, fingerprint protection off
2. Open a new private window
3. Visit a site you've never been to before

Actual result:

• For daily mail example, Shields are UP in private window
• For global settings example, global settings are not inherited

Expected result:

Shields should be DOWN in the private window... because the session content_settings should inherit from the regular content_settings

Reproduces how often:

100%

Brave version (chrome://version info)

Current master (brave/brave-core@cacede9)

[bsclifton]

cc: @bbondy for triage (I picked 1.0, but we may want to fix before then)

[LaurenWags]

Verified passed with

Brave	0.60.19 Chromium: 72.0.3626.81 (Official Build) beta(64-bit)
Revision	ac8b982e05014492d1bd7d317628a4f22a97ffa0-refs/branch-heads/3626@{#796}
OS	Mac OS X

• Verified STR from description

Verification passed on

Brave	0.60.25 Chromium: 72.0.3626.96 (Official Build) beta (64-bit)
Revision	84098ee7ef8622a9defc2ef043cd8930b617b10e-refs/branch-heads/3626@{#836}
OS	Windows 10

• Verified STR from description

Verification passed on

Brave	0.60.26 Chromium: 72.0.3626.96 (Official Build) beta(64-bit)
Revision	84098ee7ef8622a9defc2ef043cd8930b617b10e-refs/branch-heads/3626@{#836}
OS	Linux