Toolbar hide/show trigger customization

[vslavkin]

While I like the feature of hiding the toolbar, it doesn't play well with websites with buttons at the top.
It would be great to have a way to customize the trigger of the toolbar. There are usually two ways to improve the trigger of the toolbar:

1. Add a timer. If the user puts the mouse near the tab bar for 100ms or whatever, it triggers.
2. Trigger when the mouse enters the tab bar.