Limit the layout_test batch size for *SAN builds.

Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py

Index: Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py
diff --git a/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py b/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py
index aafc43f591e1bdcec60a2b66a769c50381077961..c0967d065ef4eeb7f392c5fd85f44c15491716b0 100644
--- a/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py
+++ b/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py
@@ -300,6 +300,9 @@ def parse_args(args):
 
 def _set_up_derived_options(port, options, args):
     """Sets the options values that depend on other options values."""
+    if options.batch_size is None:
+        options.batch_size = port.default_batch_size()
+
     if not options.child_processes:
         options.child_processes = os.environ.get("WEBKIT_TEST_CHILD_PROCESSES",
                                                  str(port.default_child_processes()))