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

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

 # Copyright (C) 2011 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 125 matching lines @@
                 self._port._path_to_driver(), self._port.results_directory(), profiler_name)
         else:
             self._profiler = None
 
     def __del__(self):
         self.stop()
 
     def run_test(self, driver_input, stop_when_done):
         """Run a single test and return the results.
 
-        Note that it is okay if a test times out or crashes and leaves
-        the driver in an indeterminate state. The upper layers of the program
-        are responsible for cleaning up and ensuring things are okay.
+        Note that it is okay if a test times out or crashes. content_shell
+        will be stopped when the test ends, and then restarted for the next
+        test when this function is invoked again. As part of the restart, the
+        state of Driver will be reset.
 
         Returns a DriverOutput object.
         """
         start_time = time.time()
         stdin_deadline = start_time + int(driver_input.timeout) / 2000.0
         self.start(driver_input.should_run_pixel_test, driver_input.args, stdin_deadline)
         test_begin_time = time.time()
         self.error_from_test = str()
         self.err_seen_eof = False
 
@@ skipping 357 matching lines @@
         self.decoded_content = None
         self.malloc = None
         self.js_heap = None
         self.stdin_path = None
 
     def decode_content(self):
         if self.encoding == 'base64' and self.content is not None:
             self.decoded_content = base64.b64decode(self.content)
         else:
             self.decoded_content = self.content