/usr/lib/kde4/imports/org/kde/kwin/decorations/plastik/qmldir is in kde-window-manager-common 4:4.11.8-0ubuntu6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | plugin plastikplugin
# we need to have at least one element of Qt is not able to find the plugin *shrug*
Foo 1.0 Foo.qml
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