The PositionedEventTargeting code allows input events to be dispatched to a
target not directly under the input event point. However, the coordinates of the
input event can then end up outside the bounding rect of the event target. This
state is generally unexpected by web content and may cause compatibility issues.
Fennec's front-end code used to deal with this by repositioning the input event
coordinates to be inside the bounding rect; now that Fennec is using the shared
C++ code we need to have that code here. This behaviour is guarded by a pref and
disabled by default (but enabled on Fennec).
Kartikaya Gupta
Masayuki Nakano
Ehsan Akhgari
Matt Brubeck
Robert O'Callahan