Brave ads mobile delivery policy change

[EyanGoldman]

Ads delivery policy change on mobile, will need to be taken into consideration for bat-native-ads library for brave-core.
Linked to: https://github.com/brave/browser-android-tabs/issues/1913

[LaurenWags]

Verified passed with

Brave	0.69.130 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 test plan from Brave ads mobile delivery policy change brave-core#3080
• Verified 2x per hour and 5x per hour frequencies.
• Verified switching frequency setting was honored without having to restart the browser.

Verification passed on

Brave	0.69.130 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 plan from Brave ads mobile delivery policy change brave-core#3080
• Verified 2x per hour and 5x per hour frequencies.
• Verified switching frequency setting was honored without having to restart the browser.

Verification passed on

Brave	0.69.130 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Ubuntu 18.04 LTS

• Verified test plan from Brave ads mobile delivery policy change brave-core#3080
• Verified 2x per hour and 5x per hour frequencies.
• Verified switching frequency setting was honored without having to restart the browser.