/usr/include/mirplatform/ is in libmirplatform-dev 0.21.0+16.04.20160330-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/mirplatform/mir/
/usr/include/mirplatform/mir/abnormal_exit.h
/usr/include/mirplatform/mir/graphics/
/usr/include/mirplatform/mir/graphics/buffer.h
/usr/include/mirplatform/mir/graphics/buffer_basic.h
/usr/include/mirplatform/mir/graphics/buffer_id.h
/usr/include/mirplatform/mir/graphics/buffer_properties.h
/usr/include/mirplatform/mir/graphics/cursor.h
/usr/include/mirplatform/mir/graphics/cursor_image.h
/usr/include/mirplatform/mir/graphics/display.h
/usr/include/mirplatform/mir/graphics/display_buffer.h
/usr/include/mirplatform/mir/graphics/display_configuration.h
/usr/include/mirplatform/mir/graphics/display_configuration_policy.h
/usr/include/mirplatform/mir/graphics/event_handler_register.h
/usr/include/mirplatform/mir/graphics/gl_config.h
/usr/include/mirplatform/mir/graphics/gl_context.h
/usr/include/mirplatform/mir/graphics/graphic_buffer_allocator.h
/usr/include/mirplatform/mir/graphics/platform.h
/usr/include/mirplatform/mir/graphics/platform_ipc_operations.h
/usr/include/mirplatform/mir/graphics/platform_ipc_package.h
/usr/include/mirplatform/mir/graphics/platform_operation_message.h
/usr/include/mirplatform/mir/graphics/renderable.h
/usr/include/mirplatform/mir/graphics/virtual_output.h
/usr/include/mirplatform/mir/input/
/usr/include/mirplatform/mir/input/device_capability.h
/usr/include/mirplatform/mir/input/event_builder.h
/usr/include/mirplatform/mir/input/input_device.h
/usr/include/mirplatform/mir/input/input_device_info.h
/usr/include/mirplatform/mir/input/input_device_registry.h
/usr/include/mirplatform/mir/input/input_report.h
/usr/include/mirplatform/mir/input/input_sink.h
/usr/include/mirplatform/mir/input/platform.h
/usr/include/mirplatform/mir/input/pointer_settings.h
/usr/include/mirplatform/mir/input/touchpad_settings.h
/usr/include/mirplatform/mir/module_properties.h
/usr/include/mirplatform/mir/options/
/usr/include/mirplatform/mir/options/option.h