[Telemetry] Fix idle wakeup reporting in the face of dead processes

tools/telemetry/telemetry/core/platform/process_statistic_timeline_data.py

Index: tools/telemetry/telemetry/core/platform/process_statistic_timeline_data.py
diff --git a/tools/telemetry/telemetry/core/platform/process_statistic_timeline_data.py b/tools/telemetry/telemetry/core/platform/process_statistic_timeline_data.py
new file mode 100644
index 0000000000000000000000000000000000000000..b44f03ddb5b43183088accfbcaca0e513b3440ca
--- /dev/null
+++ b/tools/telemetry/telemetry/core/platform/process_statistic_timeline_data.py
@@ -0,0 +1,58 @@
+# Copyright 2014 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.
+
+
+class ProcessStatisticTimelineData(object):
+  """Holds value of a stat for one or more processes.
+
+  This object can hold a value for more than one pid by adding another
+  object."""
+
+  def __init__(self, pid, value):
+    super(ProcessStatisticTimelineData, self).__init__()
+    assert value >= 0
+    self._value_by_pid = {pid: value}
+
+  def __sub__(self, other):
+    """The results of subtraction is an object holding only the pids contained
+    in |self|.
+
+    The motivation is that some processes may have died between two consecutive
+    measurements. The desired behavior is to only make calculations based on
+    the processes that are alive at the end of the second measurement."""
+    # pylint: disable=W0212
+    ret = self.__class__(0, 0)
+    my_dict = self._value_by_pid
+
+    ret._value_by_pid = (
+        {k: my_dict[k] - other._value_by_pid.get(k, 0) for
+            k in my_dict.keys()})

[nednguyen, 2014/08/28 15:29:00]

Shouldn't it be an error if some values are less than 0 after the subtraction? 
Also we should have timestamp info with top command, is that right? It would be
nice if __sub__ only work for later - previous. But since we will move all of
these logic to importer, so I am fine with skipping this.

+    return ret
+
+  def __add__(self, other):
+    """The result contains pids from both |self| and |other|, if duplicate
+    pids are found between objects, an error will occur. """
+    # pylint: disable=W0212
+    intersecting_pids = (set(self._value_by_pid.keys()) &
+        set(other._value_by_pid.keys()))
+    assert len(intersecting_pids) == 0
+
+    ret = self.__class__(0, 0)
+    ret._value_by_pid = {}
+    ret._value_by_pid.update(self._value_by_pid)
+    ret._value_by_pid.update(other._value_by_pid)
+    return ret
+
+  @property
+  def value_by_pid(self):
+    return self._value_by_pid
+
+  def total_sum(self):
+    """Returns the sum of all values contained by this object. """
+    return sum(self._value_by_pid.values())
+
+
+class IdleWakeupTimelineData(ProcessStatisticTimelineData):
+  """A ProcessStatisticTimelineData to hold idle wakeups."""
+  pass