Support None value for telemetry values.

tools/telemetry/telemetry/web_perf/metrics/rendering_stats.py

Index: tools/telemetry/telemetry/web_perf/metrics/rendering_stats.py
diff --git a/tools/telemetry/telemetry/web_perf/metrics/rendering_stats.py b/tools/telemetry/telemetry/web_perf/metrics/rendering_stats.py
index 33c51fb0aba2ec229763470471d01dffc439c0d3..f5c4fe9dd7c540ac0530c5c8d3dc96d2da57f970 100644
--- a/tools/telemetry/telemetry/web_perf/metrics/rendering_stats.py
+++ b/tools/telemetry/telemetry/web_perf/metrics/rendering_stats.py
@@ -1,10 +1,8 @@
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
-import logging
 from operator import attrgetter
 
-from telemetry.page import page_test
 from telemetry.web_perf.metrics import rendering_frame
 
 # These are LatencyInfo component names indicating the various components
@@ -25,19 +23,6 @@ FORWARD_SCROLL_UPDATE_COMP_NAME = (
 END_COMP_NAME = 'INPUT_EVENT_LATENCY_TERMINATED_FRAME_SWAP_COMPONENT'
 
 
-class NotEnoughFramesError(page_test.MeasurementFailure):
-  def __init__(self, frame_count):
-    super(NotEnoughFramesError, self).__init__(
-      'Only %i frame timestamps were collected ' % frame_count +
-      '(at least two are required).\n'
-      'Issues that have caused this in the past:\n' +
-      '- Browser bugs that prevents the page from redrawing\n' +
-      '- Bugs in the synthetic gesture code\n' +
-      '- Page and benchmark out of sync (e.g. clicked element was renamed)\n' +
-      '- Pages that render extremely slow\n' +
-      '- Pages that can\'t be scrolled')
-
-
 def GetInputLatencyEvents(process, timeline_range):
   """Get input events' LatencyInfo from the process's trace buffer that are
      within the timeline_range.
@@ -133,7 +118,7 @@ class RenderingStats(object):
     if HasRenderingStats(browser_process):
       timestamp_process = browser_process
     else:
-      timestamp_process  = renderer_process
+      timestamp_process = renderer_process
 
     self.frame_timestamps = []
     self.frame_times = []
@@ -177,12 +162,6 @@ class RenderingStats(object):
       self._InitFrameQueueingDurationsFromTimeline(
           renderer_process, timeline_range)
 
-    # Check if we have collected at least 2 frames in every range. Otherwise we
-    # can't compute any meaningful metrics.
-    for segment in self.frame_timestamps:
-      if len(segment) < 2:
-        raise NotEnoughFramesError(len(segment))
-
   def _InitInputLatencyStatsFromTimeline(
       self, browser_process, renderer_process, timeline_range):
     latency_events = GetInputLatencyEvents(browser_process, timeline_range)
@@ -253,5 +232,5 @@ class RenderingStats(object):
       new_frame_queueing_durations = [e.queueing_duration for e in events]
       self.frame_queueing_durations.append(new_frame_queueing_durations)
     except rendering_frame.NoBeginFrameIdException:
-      logging.warning('Current chrome version does not support the queueing '
-                      'delay metric.')
+      # Queueing delay metric is unsupported in the browser used.
+      pass