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

tools/perf/metrics/histogram_util.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 logging
-
-def SubtractHistogram(histogram_json, start_histogram_json):
-  """Subtracts a previous histogram from a histogram. Both parameters are json
-  serializations of histograms."""
-  start_histogram = json.loads(start_histogram_json)
-  # It's ok if the start histogram is empty (we had no data, maybe even no
-  # histogram at all, at the start of the test).
-  if 'buckets' not in start_histogram:
-    return histogram_json
-
-  histogram = json.loads(histogram_json)
-  if ('pid' in start_histogram and 'pid' in histogram
-      and start_histogram['pid'] != histogram['pid']):
-    raise Exception(
-        'Trying to compare histograms from different processes (%d and %d)'
-        % (start_histogram['pid'], histogram['pid']))
-
-  start_histogram_buckets = dict()
-  for b in start_histogram['buckets']:
-    start_histogram_buckets[b['low']] = b['count']
-
-  new_buckets = []
-  for b in histogram['buckets']:
-    new_bucket = b
-    low = b['low']
-    if low in start_histogram_buckets:
-      new_bucket['count'] = b['count'] - start_histogram_buckets[low]
-      if new_bucket['count'] < 0:
-        logging.error('Histogram subtraction error, starting histogram most '
-                      'probably invalid.')
-    if new_bucket['count']:
-      new_buckets.append(new_bucket)
-  histogram['buckets'] = new_buckets
-  histogram['count'] -= start_histogram['count']
-
-  return json.dumps(histogram)
-
-def GetHistogramFromDomAutomation(function, name, tab):
-  # TODO(jeremy): Remove references to
-  # domAutomationController when we update the reference builds.
-  js = ('(window.statsCollectionController ? '
-        'statsCollectionController : '
-        'domAutomationController).%s("%s")' %
-        (function, name))
-  return tab.EvaluateJavaScript(js)