In order to correctly test Qt's Device Pixel Ratio system in a 
unit test, one needs to have the QPA plugin for the platform
support reading the DEVICE_PIXEL_RATIO environment variable.

These unit tests use the "minimal" QPA plugin, which 
unfortunately does not support that variable.

The contents of this directory is a near-complete duplicate of 
"minimal" QPA plugin source from Qt, with added support for the
DEVICE_PIXEL_RATIO environment variable.

One can use this plugin as follows:

DEVICE_PIXEL_RATIO=2 QT_QPA_PLATFORM_PLUGIN_PATH=$PWD \
    QT_QPA_PLATFORM=custom qmlscene ~/tmp.qml
