[Hackerone] - Fix continuation leak in AlertPopupView

[Brandon-T]

Description

• AlertPopupView can leak the continuation when WebKit cancels the requests or starts another request while the popup is displayed.

Steps to reproduce

1. https://hackerone.com/reports/2909560

Actual result

• Popup is shown on the wrong page

Expected result

• Popup should show not show

Reproduces how often

Easily reproduced

Brave version

• All

Device/iOS version

• All

Affected browser versions

• latest AppStore
• latest TestFlight
• previous TestFlight

Reproducibility

• with Brave Shields disabled
• in the latest version of mobile Safari

Miscellaneous information

No response

[hffvld]

Verified on iPhone 14 using version(s):

Device/OS: iPhone 14 / iOS 17.7.2
Brave build: 1.75 (148)
BraveCore: 1.75.148 (132.0.6834.57)

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STEPS:

1. Follow the STR/TP from https://hackerone.com/reports/2909560
2. Verify

ACTUAL RESULTS:

• Verified that the pop-up is not shown on the wrong page.

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2025-01-06_15-39-55.mp4