1527187 - Ensure the layout viewport is always larger than the visual viewport

Status: NEW

(Core :: Panning and Zooming, enhancement, P3)

Description

[Botond Ballo [:botond]]

Once bug 1423013 and its follow-ups are all fixed (the last one that's relevant here being bug 1519013), we should be able to enforce and rely on the constraint that the layout viewport is always larger than the visual viewport.

We may have to add some special handling for the Fennec dynamic toolbar. On Fennec, the visual viewport size is based on the widget size which seems to include the toolbar height, but the layout viewport size is calculated based on the ICB size which is calculated based on the content viewer size which seems to exclude it.