Allow resizing the document pip window programmatically

[steimelchrome]

Currently (at least in the Chrome implementation), the resizeTo() and resizeBy() methods used to programmatically resize a window are disabled for document picture-in-picture windows, since there's potential for particularly annoying abuse given the always-on-top nature of the window. However, there are legitimate/useful cases for resizing a window (e.g. the user clicks to expand a playlist). In order to allow for some usage of the resize APIs while limiting its abuse potential, we should allow those APIs but consume a user gesture for each use, so the user must click on the window for it to resize