https://bugs.webkit.org/show_bug.cgi?id=119100

Reviewed by Dirk Pranke.

Introduce the WestonDriver, a Driver-implementing class that sets up an instance of Weston, the Wayland compositor,
and sets up an environment that enables the test runner to run inside it.

The design very much mimics the XvfbDriver class. It is currently used by the GTK port when the WAYLAND_DISPLAY
environment variable is set, that is when NRWT is being run under a Wayland display.

* Scripts/webkitpy/port/base.py:
(Port.to.setup_environ_for_server): Also copy the XDG_RUNTIME_DIR env from the original environment for Linux-using ports.
* Scripts/webkitpy/port/gtk.py:
(GtkPort):
(GtkPort._driver_class): Make the method memoized - the display type is not going to change during the testing, so we
should only check once for the presence of the WAYLAND_DISPLAY env and determine the proper driver class to use based on that.
(GtkPort.check_sys_deps): Call the static check_driver method on the class as returned by the _driver_class method
instead of hard-coding the XvfbDriver class in the check.
* Scripts/webkitpy/port/westondriver.py: Added.
(WestonDriver):
(WestonDriver.check_driver): Similarly to XvfbDriver, this checks for existance of the weston executable.
(WestonDriver.__init__): Again, like in XvfbDriver, we use a small delay between launching the Weston display and launching the driver.
(WestonDriver._start): Sets up the driver-specific temporary directory, launches the Weston display, sets up the environment for the
driver and then launches the driver in said environment, using the driver's Weston display.
(WestonDriver.stop): Cleans up the Weston instance and the temporary directory.
(WestonDriver._ensure_driver_tmpdir_subdirectory): A helper function that creates a subdirectory in the driver's temporary directory
and returns the absolute path to it.
* Scripts/webkitpy/port/xvfbdriver.py:
(XvfbDriver.check_driver): Renamed from check_xvfb.
(XvfbDriver._start): Access the FileSystem object through the Port's Host object, instead of the Port's private member.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153439 268f45cc-cd09-0410-ab3c-d52691b4dbfc