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diff --git a/systrace/catapult/common/py_utils/py_utils/slots_metaclass.py b/systrace/catapult/common/py_utils/py_utils/slots_metaclass.py
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+# Copyright 2017 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 SlotsMetaclass(type):
+  """This metaclass requires all subclasses to define __slots__.
+
+  Usage:
+    class Foo(object):
+      __metaclass__ = slots_metaclass.SlotsMetaclass
+      __slots__ = '_property0', '_property1',
+
+  __slots__ must be a tuple containing string names of all properties that the
+  class contains.
+  Defining __slots__ reduces memory usage, accelerates property access, and
+  prevents dynamically adding unlisted properties.
+  If you need to dynamically add unlisted properties to a class with this
+  metaclass, then take a step back and rethink your goals. If you really really
+  need to dynamically add unlisted properties to a class with this metaclass,
+  add '__dict__' to its __slots__.
+  """
+
+  def __new__(mcs, name, bases, attrs):
+    assert '__slots__' in attrs, 'Class "%s" must define __slots__' % name
+    assert isinstance(attrs['__slots__'], tuple), '__slots__ must be a tuple'
+
+    return super(SlotsMetaclass, mcs).__new__(mcs, name, bases, attrs)