Move memory-related histogram data collection to metrics/memory.py

tools/perf/metrics/histogram_util_unittest.py

-# Copyright 2013 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 json
-import unittest
-
-from metrics import histogram_util
-
-class TestHistogram(unittest.TestCase):
-  def testSubtractHistogram(self):
-    baseline_histogram = """{"count": 3, "buckets": [
-{"low": 1, "high": 2, "count": 1},
-{"low": 2, "high": 3, "count": 2}]}"""
-
-    histogram = """{"count": 14, "buckets": [
-{"low": 1, "high": 2, "count": 1},
-{"low": 2, "high": 3, "count": 3},
-{"low": 3, "high": 4, "count": 10}]}"""
-
-    new_histogram = json.loads(
-        histogram_util.SubtractHistogram(histogram, baseline_histogram))
-    new_buckets = dict()
-    for b in new_histogram['buckets']:
-      new_buckets[b['low']] = b['count']
-    self.assertFalse(1 in new_buckets)
-    self.assertEquals(1, new_buckets[2])
-    self.assertEquals(10, new_buckets[3])