shiny/driver/gldriver: Cocoa multi-screen support

Use the current screen housing the window to calculate scaling
factor and mouse events. Listen for when windows change screen
and update the geometry to match.

Change-Id: I3f05a17be16286e4c8c913cf9662899bf9c2ceaa
Reviewed-on: https://go-review.googlesource.com/13960
Reviewed-by: Rob Pike <r@golang.org>
1 file changed