Implement custom ad notification fade in/out transition

[tmancey]

No description provided.

[tmancey]

Resolved as part of #13132, please test as part of the new custom ad notifications

[btlechowski]

Verification passed on

Brave	1.26.50 Chromium: 91.0.4472.77 (Official Build) beta (64-bit)
Revision	1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS	Ubuntu 18.04 LTS

Verified fade in and fade out animations

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Verification PASSED using

Brave	1.26.52 Chromium: 91.0.4472.77 (Official Build) beta (x86_64)
Revision	1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS	macOS Version 11.4 (Build 20F71)

Steps:

1. launched Brave using --enable-logging=stderr --vmodule="*/variations/*"=6,"*/bat-native-ledger/*"=6,"*/brave_rewards/*"=6,"*/bat-native-ads/*"=6,"*/bat-native-confirmations/*"=6,"*/brave_ads/*"=9,"*/brave_user_model/*"=6 --brave-ads-staging --brave-ads-debug --rewards=staging=true,reconcile-interval=3 --variations-server-url=https://no-thanks.invalid --enable-features="AdNotifications<CommandLineStudy" --force-fieldtrials="*CommandLineStudy/Enabled" --force-fieldtrial-params="CommandLineStudy.Enabled:should_show_custom_notifications/true/ad_notification_timeout/0/ad_notification_fade_duration/2000"
2. waited (to get variations going, not sure if needed, but good step/habit)
3. shut down & restarted
4. opened a set of 4+ tabs
5. waited
6. moved cursor/pointer

Confirmed the ad faded in on display, and faded out after I clicked the [X] in the upper-right corner.

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Verification passed on

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Brave | 1.26.50 Chromium: 91.0.4472.77&nbsp;(Official Build)&nbsp;beta&nbsp;(64-bit)
-- | --
Revision | 1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS | Windows&nbsp;10 OS Version 2004 (Build 19041.985)

<!--EndFragment-->

• Verified the steps mentioned by @stephendonner above
• Followed the cmd line mentioned in https://bravesoftware.slack.com/archives/GAA4017R7/p1622822382099400?thread_ts=1622822219.099100&cid=GAA4017R7

Verified fade in and fade out animations for Ads

[GeetaSarvadnya]

Verification is NOT passed on Samsung Galaxy Tab version 10 running brave Beta build Bravemonoarm64 1.26.56.apk

• Logged a follow-up issue [ads] Add fade transition to custom notification ads on Android #16400 - Custom Ads notification fade in/out animation is not shown