/usr/include/gazebo-7/gazebo/plugins/ is in libgazebo7-dev 7.0.0+dfsg-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gazebo-7/gazebo/plugins/ActuatorPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/ArrangePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/BreakableJointPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/BuoyancyPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/CameraPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/CartDemoPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/CessnaGUIPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/CessnaPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/ContactPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/DepthCameraPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/DiffDrivePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/ElevatorPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/FollowerPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/ForceTorquePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/GpuRayPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/HydraDemoPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/HydraPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/ImuSensorPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/InitialVelocityPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/JointTrajectoryPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/LiftDragPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/LinearBatteryConsumerPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/LinearBatteryPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/ModelPropShop.hh
/usr/include/gazebo-7/gazebo/plugins/MudPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/PressurePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/RandomVelocityPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/RayPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/RaySensorNoisePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/RestApi.hh
/usr/include/gazebo-7/gazebo/plugins/RestException.hh
/usr/include/gazebo-7/gazebo/plugins/RestUiLoginDialog.hh
/usr/include/gazebo-7/gazebo/plugins/RestUiPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/RestUiWidget.hh
/usr/include/gazebo-7/gazebo/plugins/RestWebPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/RubblePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/SkidSteerDrivePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/SonarPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/SphereAtlasDemoPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/TimerGUIPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/TransporterPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/VehiclePlugin.hh
/usr/include/gazebo-7/gazebo/plugins/events/
/usr/include/gazebo-7/gazebo/plugins/events/EventSource.hh
/usr/include/gazebo-7/gazebo/plugins/events/ExistenceEventSource.hh
/usr/include/gazebo-7/gazebo/plugins/events/InRegionEventSource.hh
/usr/include/gazebo-7/gazebo/plugins/events/JointEventSource.hh
/usr/include/gazebo-7/gazebo/plugins/events/OccupiedEventSource.hh
/usr/include/gazebo-7/gazebo/plugins/events/Region.hh
/usr/include/gazebo-7/gazebo/plugins/events/RegionEventBoxPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/events/SimEventsException.hh
/usr/include/gazebo-7/gazebo/plugins/events/SimEventsPlugin.hh
/usr/include/gazebo-7/gazebo/plugins/events/SimStateEventSource.hh