Enables extensions to implement customized behavior when the user types into the browser's address bar.

When the user focuses the browser's address bar and starts typing, the browser displays a drop-down list containing suggested pages based on what they typed. This gives the user a quick way to access, for example, pages from their history or bookmarks.

The omnibox API provides the extension a way to customize the suggestions displayed in the drop-down, when the user enters a keyword defined by the extension. It works as follows:

1. First, the extension must include an "omnibox" key in its manifest.json file, which defines a keyword.
2. When the user focuses the address bar and types the keyword followed by a space, the extension gets an omnibox.onInputStarted event.
3. Optionally, the extension can call omnibox.setDefaultSuggestion() to define the first suggestion displayed in the address bar drop-down.
4. As the user continues to type characters, the extension gets omnibox.onInputChanged events. The event listener is passed the value the user has typed and can populate the address bar drop-down with suggestions. If the extension sets a default suggestion using omnibox.setDefaultSuggestion(), this suggestion is displayed first in the drop-down.
5. If the user accepts a suggestion, the extension gets an omnibox.onInputEntered event. The event listener is passed the accepted suggestion.
6. If the user deletes a suggestion, the extension gets an omnibox.onDeleteSuggestion event.
7. If the user dismisses the drop-down, the extension gets an omnibox.onInputCancelled event.