... after dwelling on preview.
Currently, the asynchronous PREVIEW_ABANDON_END action wouldn't be
ignored if the user were to have dwelled on the link that the preview is
about. The action is only ignored if the user is dwelling on the
preview, i.e. if preview.isUserDwelling is truthy.
Set preview.isUserDwelling to truthy if the user is dwelling either on
the link or on the preview.
Bug: T154923
Change-Id: I8e6989790da5884992ee9dda9e4895e2e58e6694