Raise Xvfb client limit in run_web_tests.py

Follow-up to:
https://chromium-review.googlesource.com/c/chromium/src/+/2343314
Ensure x11::Connection is only used on a single thread

Due to the above changes, content_shell now uses more X11 connections
per instance than previously. On machines with hugh numbers of cores,
this was causing run_web_tests to crash as the tests it ran tried to
more connections at a time than the default limit (256) of its Xvfb
instance allowed.

Bug: 1120107
Change-Id: Ie31fb509e91a9d7828b5f26f2b3885f857c56e24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368420
Commit-Queue: George Steel <gtsteel@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800640}

third_party/blink/tools/blinkpy/web_tests/port/linux.py

@@ -191,7 +191,7 @@ class LinuxPort(base.Port):
         self._xvfb_process = self.host.executive.popen(
             [
                 'Xvfb', display, '-screen', '0', '1280x800x24', '-ac', '-dpi',
-                '96'
+                '96', '-maxclients', '512'
             ],
             stdout=self._xvfb_stdout,
             stderr=self._xvfb_stderr,

third_party/blink/tools/blinkpy/web_tests/port/linux_unittest.py

@@ -151,7 +151,7 @@ class LinuxPortTest(port_testcase.PortTestCase, LoggingTestCase):
             ['xdpyinfo', '-display', ':99'],
             [
                 'Xvfb', ':99', '-screen', '0', '1280x800x24', '-ac', '-dpi',
-                '96'
+                '96', '-maxclients', '512'
             ],
             ['xdpyinfo'],
         ])
@@ -173,7 +173,7 @@ class LinuxPortTest(port_testcase.PortTestCase, LoggingTestCase):
             ['xdpyinfo', '-display', ':99'],
             [
                 'Xvfb', ':99', '-screen', '0', '1280x800x24', '-ac', '-dpi',
-                '96'
+                '96', '-maxclients', '512'
             ],
             ['xdpyinfo'],
         ])
@@ -203,7 +203,7 @@ class LinuxPortTest(port_testcase.PortTestCase, LoggingTestCase):
                 ['xdpyinfo', '-display', ':102'],
                 [
                     'Xvfb', ':102', '-screen', '0', '1280x800x24', '-ac',
-                    '-dpi', '96'
+                    '-dpi', '96', '-maxclients', '512'
                 ],
                 ['xdpyinfo'],
             ])
@@ -231,7 +231,7 @@ class LinuxPortTest(port_testcase.PortTestCase, LoggingTestCase):
             ['xdpyinfo', '-display', ':99'],
             [
                 'Xvfb', ':99', '-screen', '0', '1280x800x24', '-ac', '-dpi',
-                '96'
+                '96', '-maxclients', '512'
             ],
             ['xdpyinfo'],
             ['xdpyinfo'],
@@ -257,7 +257,7 @@ class LinuxPortTest(port_testcase.PortTestCase, LoggingTestCase):
             ['xdpyinfo', '-display', ':99'],
             [
                 'Xvfb', ':99', '-screen', '0', '1280x800x24', '-ac', '-dpi',
-                '96'
+                '96', '-maxclients', '512'
             ],
         ] + [['xdpyinfo']] * 51)
         env = port.setup_environ_for_server()
@@ -286,10 +286,12 @@ class LinuxPortTest(port_testcase.PortTestCase, LoggingTestCase):
         self.set_logging_level(logging.DEBUG)
 
         self.assertEqual(port.setup_test_run(), SYS_DEPS_EXIT_STATUS)
-        self.assertEqual(port.host.executive.calls, [[
-            'xdpyinfo', '-display', ':99'
-        ], ['Xvfb', ':99', '-screen', '0', '1280x800x24', '-ac', '-dpi', '96']
-                                                     ])
+        self.assertEqual(port.host.executive.calls,
+                         [['xdpyinfo', '-display', ':99'],
+                          [
+                              'Xvfb', ':99', '-screen', '0', '1280x800x24',
+                              '-ac', '-dpi', '96', '-maxclients', '512'
+                          ]])
         self.assertLog([
             'DEBUG: Starting Xvfb with display ":99".\n',
             'CRITICAL: Failed to start Xvfb on display ":99" (xvfb retcode: 3).\n'