Fix blank space in browser activity

[aibrahim-]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1212608036467427/task/1214444878566531?focus=true

Description

If a page load completes (which triggers computeBottomMarginIfNeeded), while a keyboard is being launched at the same time, there's a window where the child (browserLayout) would still be smaller in height than the parent (rootView), this would happen mid-layout and it would later match the parent size, but this causes the computeBottomMarginIfNeeded to incorrectly adjusts the browserLayout to match its parent and adds a persistent diff that is exactly the keyboard IME size.

Steps to test this PR

This is a race-condition that's hard to replicate, so it will need mutliple tries. also for some-reason enabling native-input with the toggle disabled makes it easier to repro.

• open a new website.
• try to open the keyboard by tapping the address bar as the page is about to finish loading.

I was able to verify the fix by having a log in the if statement added here, this log always triggers when the bug repros, and with the fix in place, the bug doesn't repro anymore.

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Note

Low Risk
Low risk: small, localized guard in CoordinatorLayoutHelper.computeBottomMarginIfNeeded to avoid applying an incorrect margin during an IME/layout race; main risk is skipping a needed margin update in some edge cases until the next layout pass.

Overview
Prevents a race where computeBottomMarginIfNeeded could permanently add the keyboard (IME) height to the child view’s bottomMargin while the parent is mid-resize.

The method now snapshots childHeight/parentHeight and bails out when the child reports a height larger than the parent, without updating lastYPosition, so a later call can recompute once layout has settled.

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