The current implementation of the views omnibox is complex.
When a user types in the omnibox, a popup is shown. There are two implementations of the popup: a webui version adapted from the realbox popup and a views version. Currently the views version is live.
A hole is cut in the popup to allow the original textbox of the omnibox to peek through. Historically, the popup was just a rectanglular view placed below the textfield. The hole exists because in the 10th birthday UI refresh the design changed to surround the text field rather than just appearing below it.