Notifications are not shown from the background

[NejcZdovc]

This PR broke browser tests brave/brave-core#2296. We need to fix it.

What is happening under the hood is basically observers are not triggered, meaning that user will only get notification when they click on the BAT logo. They will not get notification from the background.

[GeetaSarvadnya]

Verification passed on

Brave	0.63.47 Chromium: 74.0.3729.108 (Official Build) (64-bit)
Revision	daaff52abef89988bf2a26091062160b1482b108-refs/branch-heads/3729@{#901}
OS	Windows 10 OS Build 17134.523

• Verified the test plan from Adds Brave Ads launch notification for existing Rewards users brave-core#1365

Verification passed with

Brave	0.63.47 Chromium: 74.0.3729.108 (Official Build) (64-bit)
Revision	daaff52abef89988bf2a26091062160b1482b108-refs/branch-heads/3729@{#901}
OS	Mac OS X

• Verified the test plan from Adds Brave Ads launch notification for existing Rewards users brave-core#1365

[kjozwiak]

We'll need to retest this once brave/brave-core#2318 lands into 0.63.x and a new RC3 has been created.

[btlechowski]

Verification passed on

Brave	0.63.48 Chromium: 74.0.3729.108 (Official Build) (64-bit)
Revision	daaff52abef89988bf2a26091062160b1482b108-refs/branch-heads/3729@{#901}
OS	Ubuntu 18.04 LTS

Used test plan from brave/brave-core#2318. Enabled rewards from panel and brave://rewards

brave/brave-core#1365 is blocked on Linux due to #4202

Verification passed on

Brave	0.63.48 Chromium: 74.0.3729.108 (Official Build) (64-bit)
Revision	daaff52abef89988bf2a26091062160b1482b108-refs/branch-heads/3729@{#901}
OS	Windows 10 OS Build 17134.523

• Verified the test plan from Fixes rewards bug and also browser tests (uplift to 0.63.x) brave-core#2318

Verified passed with

Brave	0.63.48 Chromium: 74.0.3729.108 (Official Build) (64-bit)
Revision	daaff52abef89988bf2a26091062160b1482b108-refs/branch-heads/3729@{#901}
OS	Mac OS X

• Verified test plan from Fixes browser tests brave-core#2315
• Verified that notification to enable Ads displays with 0.63.48 whether Rewards were enabled via panel or brave://rewards page in previous profile.
• Additionally, verified additional notifications (UGP grant, auto contribute, ad grant) were displayed.