background: Scale monitor_area after texture creation
Scaling the monitor_area
before texture creation was just wasting
megabytes of memory on resolution that the monitor can't display. This
was also hurting runtime performance.
Example:
Monitor is natively 1920x1080 and scale set to 3.
Before: The monitor texture allocated was 5760x3250x4 = 74.6 MB
After: The monitor texture allocated is 1920x1080x4 = 8.3 MB
Closes: gnome-shell#2118 (closed)