Add mozlog logger that goes via a queue,

This allows subprocesses to log to a shared stream via a queue, so that we
avoid the overhead of a multiprocessing Lock around all log access, but still
avoid races where two processes try to log simultaneously. It's mostly useful
where one process is responsible for the majority of logging, but some messages
will be generated in child processes.

MozReview-Commit-ID: ABl6cvpb6qI

Upstreamed from https://bugzilla.mozilla.org/show_bug.cgi?id=1368342 [ci skip]

Author: jgraham

tools/wptrunner/wptrunner/environment.py

@@ -6,7 +6,7 @@
 import sys
 import time
 
-from mozlog import get_default_logger, handlers
+from mozlog import get_default_logger, handlers, proxy
 
 from wptlogging import LogLevelRewriter
 
@@ -168,6 +168,8 @@ def setup_server_logging(self):
         log_filter = LogLevelRewriter(log_filter, ["error"], "warning")
         server_logger.component_filter = log_filter
 
+        server_logger = proxy.QueuedProxyLogger(server_logger)
+
         try:
             #Set as the default logger for wptserve
             serve.set_logger(server_logger)