Add extra content_shell per worker for virtual tests, except on Android.

Tools/Scripts/webkitpy/layout_tests/port/base.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 251 matching lines @@
         """Return the default batch size to use for this port."""
         if self.get_option('enable_sanitizer'):
             # ASAN/MSAN/TSAN use more memory than regular content_shell. Their
             # memory usage may also grow over time, up to a certain point.
             # Relaunching the driver periodically helps keep it under control.
             return 40
         # The default is infinte batch size.
         return None
 
     def default_child_processes(self):
-        """Return the number of drivers to use for this port."""
+        """Return the number of child processes to use for this port."""
         return self._executive.cpu_count()
 
+    def max_drivers_per_process(self):
+        """The maximum number of drivers a child process can use for this port."""
+        return 2
+
     def default_max_locked_shards(self):
         """Return the number of "locked" shards to run in parallel (like the http tests)."""
         max_locked_shards = int(self.default_child_processes()) / 4
         if not max_locked_shards:
             return 1
         return max_locked_shards
 
     def baseline_path(self):
         """Return the absolute path to the directory to store new baselines in for this port."""
         # FIXME: remove once all callers are calling either baseline_version_dir() or baseline_platform_dir()
@@ skipping 1478 matching lines @@
 class PhysicalTestSuite(object):
     def __init__(self, base, args, reference_args=None):
         self.name = base
         self.base = base
         self.args = args
         self.reference_args = args if reference_args is None else reference_args
         self.tests = set()
 
     def __repr__(self):
         return "PhysicalTestSuite('%s', '%s', %s, %s)" % (self.name, self.base, self.args, self.reference_args)