[Telemetry] Add a profiler based loading measurement.

tools/telemetry/telemetry/page/csv_page_measurement_results.py

Index: tools/telemetry/telemetry/page/csv_page_measurement_results.py
diff --git a/tools/telemetry/telemetry/page/csv_page_measurement_results.py b/tools/telemetry/telemetry/page/csv_page_measurement_results.py
index bd2e8d291193ee2e98f4006c6e610f681615c82b..2440dd86e736038470694a948fb22cde64b549d5 100644
--- a/tools/telemetry/telemetry/page/csv_page_measurement_results.py
+++ b/tools/telemetry/telemetry/page/csv_page_measurement_results.py
@@ -7,9 +7,10 @@ from telemetry.page import page_measurement_results
 
 class CsvPageMeasurementResults(
     page_measurement_results.PageMeasurementResults):
-  def __init__(self, output_stream, output_after_every_page):
+  def __init__(self, output_stream=None, output_after_every_page=None):
     super(CsvPageMeasurementResults, self).__init__()
-    self._results_writer = csv.writer(output_stream)
+    if output_stream:
+      self._results_writer = csv.writer(output_stream)
     self._did_output_header = False
     self._header_names_written_to_writer = None
     self._output_after_every_page = output_after_every_page