Add check for overlapped record ranges.

tools/telemetry/telemetry/web_perf/metrics/timeline_based_metric.py

Index: tools/telemetry/telemetry/web_perf/metrics/timeline_based_metric.py
diff --git a/tools/telemetry/telemetry/web_perf/metrics/timeline_based_metric.py b/tools/telemetry/telemetry/web_perf/metrics/timeline_based_metric.py
index 0a4f56e7c152035ef981154f682986952c287687..e37a1f80a385e8bec0a7d22ba0e78ae7940c0318 100644
--- a/tools/telemetry/telemetry/web_perf/metrics/timeline_based_metric.py
+++ b/tools/telemetry/telemetry/web_perf/metrics/timeline_based_metric.py
@@ -3,7 +3,31 @@
 # found in the LICENSE file.
 
 
+class TimelineBasedMetricException(Exception):
+  """Exception that can be thrown from metrics that implements
+     TimelineBasedMetric to indicate a problem arised when computing the metric.
+     """
+
+
+def _TimeRangesHasOverlap(iterable_time_ranges):
+  """ Returns True if there is are overlapped ranges in time ranges.
+  iterable_time_ranges: an iterable of time ranges. Each time range is a
+  tuple (start time, end time).
+  """
+  # Sort the ranges by the start time
+  sorted_time_ranges = sorted(iterable_time_ranges)
+  last_range = sorted_time_ranges[0]
+  for current_range in sorted_time_ranges[1:]:
+    start_current_range = current_range[0]
+    end_last_range = last_range[1]
+    if start_current_range < end_last_range:
+      return True
+    last_range = current_range
+  return False
+
+
 class TimelineBasedMetric(object):
+
   def __init__(self):
     """Computes metrics from a telemetry.core.timeline Model and a range
 
@@ -16,9 +40,20 @@ class TimelineBasedMetric(object):
     The override of this method should compute results on the data **only**
     within the interaction_records' start and end time ranges.
 
-    model is an instance of telemetry.core.timeline.model.TimelineModel.
-    interaction_records is a list of instances of TimelineInteractionRecord.
-    results is an instance of page.PageTestResults.
+    Args:
+      model: An instance of telemetry.core.timeline.model.TimelineModel.
+      interaction_records: A list of instances of TimelineInteractionRecord. If
+        the override of this method doesn't support overlapped ranges, use
+        VerifyNonOverlappedRecords to check that no records are overlapped.
+      results: An instance of page.PageTestResults.
 
     """
     raise NotImplementedError()
+
+  def VerifyNonOverlappedRecords(self, interaction_records):
+    """This raises exceptions if interaction_records contain overlapped ranges.
+    """
+    if _TimeRangesHasOverlap(((r.start, r.end) for r in interaction_records)):
+      raise TimelineBasedMetricException(
+          'This metric does not support interaction records with overlapped '
+          'time range.')