Brave Ads crash when the browser enters the background

[tmancey]

https://brave.sp.backtrace.io/p/brave/debug?time=all&filters=(_deleted%3D0%2C(ver%2Cregex%2C%22(87.1%7C86.1%7C85.1)%22)%2C(callstack%2Cregex%2C%22(BatAds%7CAdsService%7CAdsImpl%7CConfirmationsImpl)%22))&fingerprint=49208421bd2c5b9235343bb5a46bd316f22881e35eaf4730e93abcda928a16ca

[00] ads::Log
[01] ads::AdsImpl::OnBackground
[02] bat_ads::mojom::BatAdsStubDispatch::Accept
[03] mojo::InterfaceEndpointClient::HandleValidatedMessage
[04] mojo::MessageDispatcher::Accept
[05] mojo::internal::MultiplexRouter::ProcessIncomingMessage
[06] mojo::internal::MultiplexRouter::Accept
[07] mojo::Connector::DispatchMessage
[08] mojo::Connector::ReadAllAvailableMessages
[09] base::sequence_manager::internal::ThreadControllerWithMessagePumpImpl::DoWorkImpl
[10] base::sequence_manager::internal::ThreadControllerWithMessagePumpImpl::DoWork
[11] base::MessagePumpDefault::Run
[12] base::sequence_manager::internal::ThreadControllerWithMessagePumpImpl::Run
[13] content::UtilityMain
[14] content::ContentMainRunnerImpl::Run
[15] service_manager::Main
[16] content::ContentMain
[17] ChromeMain
[18] main

[tmancey]

@jsecretan this issue occurs if the user backgrounds the browser while the browser is shutting down.

This crash just takes down the ads service, which is restarted.

[btlechowski]

Verification passed on

Brave	1.17.59 Chromium: 86.0.4240.183 (Official Build) dev (64-bit)
Revision	0b568b034b8f7994697cb341eeca5979b84151cc-refs/branch-heads/4240@{#1374}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#6815
Verified no crash. Verified 4 times.

Verification passed on

Brave	1.17.62 Chromium: 86.0.4240.185 (Official Build) dev (64-bit)
Revision	37e6f852ed18086458552039ad26421aa9fc7acc-refs/branch-heads/4240@{#1377}
OS	Windows 7 Service Pack 1 (Build 7601.24544)

Verified test plan from brave/brave-core#6815
Verified no crash. Verified 7 times.

---

Verified passed with

Brave | 1.17.69 Chromium: 87.0.4280.60 (Official Build) (x86_64)
-- | --
Revision | 12697cfeb273d7de95cf9b18350d2c457f58224c-refs/branch-heads/4280@{#1352}
OS | macOS Version 10.14.6 (Build 18G6042)

Verified test plan from brave/brave-core#6815
No crash observed. Ran thru test plan 10+ times.