The fix used for iOS (keep a queue of preloaded web views) isn't appropriate
for macOS since the first view is used immediately. That approach would
solve the flash of white when first searching, but not the flash of white
when launching the application.
Instead, use a modification of the original solution used for iOS:
- wrap the web view in a box with an appropriate background color
- hide the web view at creation
- show the web view after* the first load
This doesn't suffer the latency problem that the same solution on iOS had
because the first load is always local, "No Selection" HTML.
[*] Showing the view immediately after the first load still causes the flash
to white. Waiting 0.05 seconds avoids this. That's a fairly terrible hack,
but I don't have a better solution at present.
