telemetry: Remove gaps between interactions when calculating smoothness metrics.

BUG=477757

Review URL: https://codereview.chromium.org/1092803002

Cr-Commit-Position: refs/heads/master@{#325583}

tools/telemetry/telemetry/web_perf/metrics/smoothness.py

@@ -88,6 +88,21 @@ class SmoothnessMetric(timeline_based_metric.TimelineBasedMetric):
                 if d / refresh_period >= min_normalized_delta]
     return (deltas, [delta / refresh_period for delta in deltas])
 
+  @staticmethod
+  def _JoinTimestampRanges(frame_timestamps):
+    """Joins ranges of timestamps, adjusting timestamps to remove deltas
+    between the start of a range and the end of the prior range.
+    """
+    timestamps = []
+    for timestamp_range in frame_timestamps:
+      if len(timestamps) == 0:
+        timestamps.extend(timestamp_range)
+      else:
+        for i in range(1, len(timestamp_range)):
+          timestamps.append(timestamps[-1] +
+              timestamp_range[i] - timestamp_range[i-1])
+    return timestamps
+
   def _ComputeSurfaceFlingerMetric(self, page, stats):
     jank_count = None
     avg_surface_fps = None
@@ -95,7 +110,7 @@ class SmoothnessMetric(timeline_based_metric.TimelineBasedMetric):
     frame_lengths = None
     none_value_reason = None
     if self._HasEnoughFrames(stats.frame_timestamps):
-      timestamps = FlattenList(stats.frame_timestamps)
+      timestamps = self._JoinTimestampRanges(stats.frame_timestamps)
       frame_count = len(timestamps)
       milliseconds = timestamps[-1] - timestamps[0]
       min_normalized_frame_length = 0.5

tools/telemetry/telemetry/web_perf/metrics/smoothness_unittest.py

@@ -60,17 +60,29 @@ class SmoothnessMetricUnitTest(unittest.TestCase):
         self.not_enough_frames_timestamps)
     self.assertFalse(has_enough_frames)
 
-  def testComputeSurfaceFlingerMetric(self):
+  def testComputeSurfaceFlingerMetricNoJank(self):
     stats = _MockRenderingStats(refresh_period=10,
-                                frame_timestamps=self.good_timestamps,
-                                frame_times=[[10, 20], [30, 40, 50]])
+                                frame_timestamps=[[10, 20], [130, 140, 150]],
+                                frame_times=[[10], [10, 10]])
     avg_surface_fps, jank_count, max_frame_delay, frame_lengths = (
         self.metric._ComputeSurfaceFlingerMetric(self.page, stats))
-    self.assertEquals([1, 1, 1, 1], frame_lengths.values)
+    self.assertEquals([1, 1, 1], frame_lengths.values)
     self.assertEquals(1, max_frame_delay.value)
     self.assertEquals(0, jank_count.value)
     self.assertEquals(100, avg_surface_fps.value)
 
+  def testComputeSurfaceFlingerMetricJank(self):
+    stats = _MockRenderingStats(
+        refresh_period=10,
+        frame_timestamps=[[10, 20, 50], [130, 140, 150, 170, 180]],
+        frame_times=[[10, 30], [10, 10, 20, 10]])
+    avg_surface_fps, jank_count, max_frame_delay, frame_lengths = (
+        self.metric._ComputeSurfaceFlingerMetric(self.page, stats))
+    self.assertEquals([1, 3, 1, 1, 2, 1], frame_lengths.values)
+    self.assertEquals(3, max_frame_delay.value)
+    self.assertEquals(2, jank_count.value)
+    self.assertEquals(67, avg_surface_fps.value)
+
   def testComputeFrameTimeMetricWithNotEnoughFrames(self):
     stats = _MockRenderingStats(
         refresh_period=10,