[macOS] Fix DeallocationTests crash with CSS 14.0.0

[mallexxx]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1202406491309510/task/1214067738586364
Tech Design URL: N/A
CC: N/A

Description

• DeallocationTests.testWhenLastTabClosed_windowIsDeallocated was navigating to https://duckduckgo.com (via .duckDuckGo content) without a TestSchemeHandler, triggering the Tab.willStart() integration-test navigation guard added in Nov 2025 — replaced with data: URLs, matching the approach already used by the sibling test testWindowsDeallocation()
• NewTabPageOmnibarActionsHandlerTests (previously a dangling file not compiled into any target) now compiles: fixed submitChat calls to include the required modelId/images parameters, corrected testViewAllAiChats_opensNewAIChatTab to use .newTab target (was .sameTab but asserting 2 tabs), and added firedPixels = [] to tearDown to satisfy the test isolation checker

Testing Steps

• Run DeallocationTests/testWhenLastTabClosed_windowIsDeallocated in the Integration Tests target — should pass without SIGTRAP
• Run all NewTabPageOmnibarActionsHandlerTests — all 9 tests should pass

Impact and Risks

Impact Level: Low

What could go wrong?

• testWhenLastTabClosed_windowIsDeallocated used .duckDuckGo intentionally to test window deallocation with a "real" URL content type — replacing with data: means it no longer exercises that exact code path, but deallocation behaviour is the same regardless of URL scheme

Quality Considerations

• Test-only change; no production code modified
• Both test classes verified passing locally (run together in sequence to confirm test isolation)

Notes to Reviewer

The root crash: CSS 14.0.0 NTP JavaScript triggers a real https://duckduckgo.com navigation during page initialisation. Any integration test that creates a window/tab loading the NTP without a registered TestSchemeHandler will hit Tab.willStart()'s fatalError. The fix for DeallocationTests is minimal and matches the existing pattern in the same file.

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Note

Low Risk
Test-only changes that adjust fixtures and expectations; minimal risk outside potential CI behavior differences due to the new data: URL loading path.

Overview
Fixes macOS integration-test instability by updating DeallocationTests.testWhenLastTabClosed_windowIsDeallocated to open windows with a data: URL instead of .duckDuckGo, avoiding real navigation side effects during CI.

Also wires NewTabPageOmnibarActionsHandlerTests into the Xcode test target and updates the tests to match current APIs (adds modelId/images args), corrects the viewAllAiChats open target to .newTab, and resets firedPixels in tearDown for test isolation.

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