Fix initial region location for High DPI screens
Review Request #129190 - Created Oct. 15, 2016 and submitted
QML dimensions are measured in device-independent pixels, be sure to make appropriate conversions. Also make sure that the new selection size feature displays the correct dimensions. Tested with: QT_SCALE_FACTOR=2 src/spectacle and dragging the region. CCBUG: 357022
Testing per above, but the bug cannot be closed yet (will comment on that bug).