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

tools/perf/metrics/histogram_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
+from metrics import histogram
 
 class TestHistogram(unittest.TestCase):
   def testSubtractHistogram(self):
     baseline_histogram = """{"count": 3, "buckets": [
-{"low": 1, "high": 2, "count": 1},
-{"low": 2, "high": 3, "count": 2}]}"""
+        {"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}]}"""
+    later_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))
+        histogram.SubtractHistogram(later_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])