Simplify LayoutMetric.

tools/telemetry/telemetry/web_perf/metrics/layout.py

Index: tools/telemetry/telemetry/web_perf/metrics/layout.py
diff --git a/tools/telemetry/telemetry/web_perf/metrics/layout.py b/tools/telemetry/telemetry/web_perf/metrics/layout.py
index baa5295a7aa2a35b73531b03dd292c87b8b76074..558a9744d0bcbc3a898208820c68398eec5e623b 100644
--- a/tools/telemetry/telemetry/web_perf/metrics/layout.py
+++ b/tools/telemetry/telemetry/web_perf/metrics/layout.py
@@ -3,55 +3,41 @@
 # found in the LICENSE file.
 
 import math
-from telemetry.value import scalar
+from telemetry.value import list_of_scalar_values
 from telemetry.web_perf.metrics import timeline_based_metric
 
 
 class LayoutMetric(timeline_based_metric.TimelineBasedMetric):
-  """Computes metrics that measure layout performance, specifically,
-  avg and stddev of CPU time of layout-related trace events:
+  """Reports directly durations of FrameView::performLayout events.
 
-    layout_total_{avg,stddev}: FrameView::layout
-    layout_{avg,stddev}: FrameView::performLayout
-    pre_layout_{avg,stddev}: FrameView::performPreLayoutTasks
-    post_layout_{avg,stddev}: FrameView::performPostLayoutTasks
-    layer_positions_{avg,stddev}: RenderLayer::updateLayerPositionsAfterLayout
+    layout: Durations of FrameView::performLayout events that were caused by and
+            start during user interaction.
 
   Layout happens no more than once per frame, so per-frame-ness is implied.
-  Not all pages have interactions, so interaction records are not required.
   """
-  EVENTS = {
-    'FrameView::layout': 'layout_total',
-    'FrameView::performLayout': 'layout',
-    'FrameView::performPreLayoutTasks': 'pre_layout',
-    'FrameView::performPostLayoutTasks': 'post_layout',
-    'RenderLayer::updateLayerPositionsAfterLayout': 'layer_positions',
-  }
+  EVENT_NAME = 'FrameView::performLayout'
 
   def __init__(self):
     super(LayoutMetric, self).__init__()
 
-  def AddResults(self, _model, renderer_thread, _interaction_records, results):
-    self._AddResults(renderer_thread.parent.IterAllSlices(), results)
-
-  def _AddResults(self, events, results):
-    metrics = dict((long_name, (short_name, [])) for long_name, short_name in
-        self.EVENTS.iteritems())
+  def AddResults(self, _model, renderer_thread, interactions, results):
+    assert interactions
+    self._AddResultsInternal(renderer_thread.parent.IterAllSlices(),
+                             interactions, results)
 
+  def _AddResultsInternal(self, events, interactions, results):
+    layouts = []
     for event in events:
-      if event.name in metrics:
-        metrics[event.name][1].append(event.end - event.start)
-
-    for long_name, (short_name, durations) in metrics.iteritems():
-      count = len(durations)
-      avg = 0.0
-      stddev = 0.0
-      if count:
-        avg = sum(durations) / count
-        stddev = math.sqrt(sum((d - avg) ** 2 for d in durations) / count)
-      results.AddValue(scalar.ScalarValue(results.current_page,
-          short_name + '_avg', 'ms', avg,
-          description='Average duration of %s events' % long_name))
-      results.AddValue(scalar.ScalarValue(results.current_page,
-          short_name + '_stddev', 'ms', stddev,
-          description='stddev of duration of %s events' % long_name))
+      if (event.name == self.EVENT_NAME) and any(
+              interaction.start <= event.start <= interaction.end
+              for interaction in interactions):
+        layouts.append(event.end - event.start)
+    if not layouts:
+      return
+    results.AddValue(list_of_scalar_values.ListOfScalarValues(
+      page=results.current_page,
+      name='layout',
+      units='ms',
+      values=layouts,
+      description=('List of durations of layouts that were caused by and '
+                   'start during interactions')))