[Stats Refresh] StatsViewModels: Replace default search engine icon

[frosty]

Refs #11080.

I took an attempt at replacing the search engine icon with a Gridicon as referenced in the issue above.

I figured the view model would be the best place for it, as that's all about transforming the data into the correct format to view. I also opted to switch on the existing icon URL filename instead of the referrer title, as I thought that would change for different locales.

I don't love that it's duplicated in two places, although the rest of the method is already duplicated. If we were to use this in more places, then maybe extracting it somewhere else would make sense. But if you have any suggestions for improvements, or you'd tackle this a different way, let me know!

Before

After

To test:

• Build and run, navigate to search referrers in Stats, and check it looks as above.

[ScoutHarris]

Hey @frosty .

The only issue is the image is a bit too big.

StatsTotalRow bases the image size on what type it is. Since you're using the icon parameter, the image size is 24x24. The Referrer icons are meant to be 20x20, which is intrinsic to the socialIconURL param.

The complication is that, before this, all Referrer icons were downloaded, and thus the size is tied to this bit of logic, in StatsTotalRow.configureIcon:

        if let iconURL = rowData.socialIconURL {
            imageWidthConstraint.constant = Constants.socialImageSize
            downloadImageFrom(iconURL)
        }

[ScoutHarris]

I'll go ahead and approve this. I'll address the image size issue separately.