[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..028ad5210b51de4437244515d8008a7f4c821ba7
--- /dev/null
+++ b/tools/telemetry/telemetry/web_perf/metrics/memory_timeline.py
@@ -0,0 +1,40 @@
+# 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.
+
+from telemetry.timeline import memory_dump_event
+from telemetry.value import list_of_scalar_values
+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_stats = [memory_dump.GetStatsSummary()
+                    for memory_dump in model.IterMemoryDumpEvents()
+                    if with_mmaps_during_interactions(memory_dump)]
+
+    if memory_stats:
+      none_reason = None
+    else:
+      none_reason = 'No memory dumps found during test interactions'
+
+    for metric in REPORTED_METRICS:
+      values = [d[metric] for d in memory_stats] if memory_stats else None
+      results.AddValue(list_of_scalar_values.ListOfScalarValues(
+          page=results.current_page,
+          name='memory_' + metric,
+          units='bytes',
+          values=values,
+          none_value_reason=none_reason))