def StartTracing(self, custom_categories=None,
                  timeout=web_contents.DEFAULT_WEB_CONTENTS_TIMEOUT):
   """ custom_categories is an optional string containing a list of
   comma separated categories that will be traced instead of the
   default category set.  Example: use
   "webkit,cc,disabled-by-default-cc.debug" to trace only those three
   event categories.
   """
   if self._tracing_backend is None:
     self._tracing_backend = tracing_backend.TracingBackend(self._port)
   return self._tracing_backend.StartTracing(custom_categories, timeout)
 def StartTracing(self, trace_options, custom_categories=None,
                  timeout=web_contents.DEFAULT_WEB_CONTENTS_TIMEOUT):
   """
   Args:
       trace_options: An tracing_options.TracingOptions instance.
       custom_categories: An optional string containing a list of
                        comma separated categories that will be traced
                        instead of the default category set.  Example: use
                        "webkit,cc,disabled-by-default-cc.debug" to trace only
                        those three event categories.
   """
   assert trace_options and trace_options.enable_chrome_trace
   if self._tracing_backend is None:
     self._tracing_backend = tracing_backend.TracingBackend(self._port, self)
   return self._tracing_backend.StartTracing(
       trace_options, custom_categories, timeout)