Summary: The original Popover component doesn't work when the popover goes out of bounds of the current container, and overflow is not visible, which is the case in the title bar. This changes it to use a new absolutely positioned one instead. Reviewed By: mweststrate Differential Revision: D22724110 fbshipit-source-id: f41b6d154ccb66a94b63533fe9c30d2a2c49f1db