fix: avoid redundant page-favicon-updated events on setBounds

[ANANYA542]

Description of Change

Closes #49392

Fixes an issue where calling setBounds on a WebContentsView unintentionally triggers the page-favicon-updated event even when the favicon has not actually changed.

Currently, layout-related updates such as resizing or repositioning a WebContentsView can cause redundant emissions of page-favicon-updated, which is unexpected and leads to duplicate callbacks in user code. This change ensures that the event is only emitted when there is a real change in the favicon data, preventing unnecessary and misleading notifications.

This makes the page-favicon-updated event more semantically correct and avoids side effects caused by purely visual or layout updates.

Checklist

• [ x] PR description included
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• tests are changed or added
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Release Notes

Notes: Fixed an issue where calling setBounds on a WebContentsView could trigger redundant page-favicon-updated events even when the favicon had not changed.

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[codebytere]

Confirmed this corrects the issue. Please add a test here to validate the fix. You also need to sign your commit.

[codebytere]

Suggested change

	// Deduplicate: only emit if favicon URLs actually changed
	// Only emit if favicon URLs actually changed

[nikwen]

I wonder if this just works around an upstream issue that should really be fixed in Chromium. Why would WebContentsObserver::DidUpdateFaviconURL be called in the first place when changing bounds?

[ckerr]

(nit) Needs #include "base/containers/flat_set.h" at the top of the header file