refactor: handle onRenderProcessGone in image preview

[criticalAY]

Purpose / Description

• Startup failure: InvocationTargetException: Cannot call WebViewCachedFlags.init more than once. #21529 shows users a Chromium assert, Cannot call WebViewCachedFlags.init more than once, which says nothing about why their app won't start. Android doesn't cache a failed WebView load, so our second WebView call re-runs Chromium's provider constructor and dies on re-entry, while the first failure, the real one, was already thrown away. This keeps the first failure so the crash report actually tells us what broke.

Fixes

• Related to Startup failure: InvocationTargetException: Cannot call WebViewCachedFlags.init more than once. #21529

Approach

See commit

How Has This Been Tested?

Unit testing

Learning (optional, can help others)

NA

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[david-allison]

LGTM, cheers!

nit: non-blocker. destroy isn't called in this activity; probably one for a quick issue

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timebox another couple days for a second reviewer, then let's merge