xvfb: weston: Set size for virtual display

By default, the size of the virtual display that
Weston size is quite small and some browser_tests
(not part of the Wayland tester yet) fail because
of their expectations of windows' vs screen's bounds.

Thus, set the size to be 1920x1080, which adequate
enough and gives plenty of room to manage sizes of
windows.

Bug: 1022750
Change-Id: I4c90b9923431b533020fb63f8a9eb0153823a451
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207199
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770628}

testing/xvfb.py

@@ -230,8 +230,12 @@ def _run_with_weston(cmd, env, stdoutfile):
       # to enter idle state. Otherwise, Weston stops to send frame callbacks,
       # and tests start to time out (this typically happens after 300 seconds -
       # the default time after which Weston enters the idle state).
+      # 3) --width && --height set size of a virtual display: we need to set
+      # an adequate size so that tests can have more room for managing size
+      # of windows.
       weston_proc = subprocess.Popen(
-         ('./weston', '--backend=headless-backend.so', '--idle-time=0'),
+         ('./weston', '--backend=headless-backend.so', '--idle-time=0',
+          '--width=1024', '--height=768'),
          stderr=subprocess.STDOUT, env=env)
 
       # Get the $WAYLAND_DISPLAY set by Weston and pass it to the test launcher.