[Telemetry] Adding Memory Timeline Metric

tools/telemetry/telemetry/web_perf/metrics/memory_timeline.py

Index: tools/telemetry/telemetry/web_perf/metrics/memory_timeline.py
diff --git a/tools/telemetry/telemetry/web_perf/metrics/memory_timeline.py b/tools/telemetry/telemetry/web_perf/metrics/memory_timeline.py
new file mode 100644
index 0000000000000000000000000000000000000000..7a33e341ba0bdd9bb59470a919bd23c97c97ed6d
--- /dev/null
+++ b/tools/telemetry/telemetry/web_perf/metrics/memory_timeline.py
@@ -0,0 +1,52 @@
+# Copyright 2015 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 telemetry.timeline import memory_dump_event
+from telemetry.value import scalar as scalar_value
+from telemetry.web_perf.metrics import timeline_based_metric
+
+
+REPORTED_METRICS = memory_dump_event.STATS_SUMMARY.keys()
+
+
+class MemoryTimelineMetric(timeline_based_metric.TimelineBasedMetric):
+  """MemoryTimelineMetric reports summary stats from memory dump events."""
+
+  def AddResults(self, model, _renderer_thread, interactions, results):
+    def contained_in(dump, interaction):
+      return interaction.start < dump.start and dump.end < interaction.end
+
+    def with_mmaps_during_interactions(dump):
+      return dump.has_mmaps and any(contained_in(dump, interaction)
+                                    for interaction in interactions)
+
+    memory_dump_events = model.IterMemoryDumpEvents(reverse=True)
+    try:
+      # We report the latest dump that happened during the interactions.
+      # Assumes that memory dump events are sorted in increasing time order.
+      memory_dump = next(memory_dump
+                         for memory_dump in memory_dump_events
+                         if with_mmaps_during_interactions(memory_dump))
+    except StopIteration:
+      memory_dump = None
+
+    if memory_dump:
+      stats = memory_dump.GetStatsSummary()
+      none_reason = None
+      logging.info('%s %s', results.current_page, stats)
+    else:
+      # No memory dumps found, return None values for all metrics.
+      stats = dict.fromkeys(REPORTED_METRICS)
+      none_reason = 'No memory dumps found during test interactions'
+      logging.warning('No memory dumps found for %s', results.current_page)
+
+    for name, value in stats.iteritems():
+      results.AddValue(scalar_value.ScalarValue(
+          page=results.current_page,
+          name='memory_infra_' + name,
+          units='bytes',
+          value=value,
+          none_value_reason=none_reason))