Add uma stats to help evaluate the impact of changes to the quota allocation logic.

storage/common/storage_histograms.cc

+// 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.
+
+#include "storage/common/storage_histograms.h"
+
+#include "base/metrics/histogram_macros.h"
+
+namespace storage {
+
+namespace {
+
+base::HistogramBase* GetBytesCountHistogram(const std::string& name) {
+  const int kMin = 1;
+  const int kMax = 10000000;
+  const int kNumBuckets = 50;
+  return base::Histogram::FactoryGet(
+      name, kMin, kMax, kNumBuckets,
+      base::Histogram::kUmaTargetedHistogramFlag);

[Ilya Sherman, 2017/05/19 00:17:14]

nit: Could you use base::UmaHistogramCustomCounts here?

[michaeln, 2017/05/19 01:22:05]

yes, thats much better, thank you :)

+}
+
+}  // anonomous namespace
+
+void RecordBytesWritten(const char* label, int amount) {
+  std::string name("Storage.BytesWritten.");
+  name.append(label);

[Ilya Sherman, 2017/05/19 00:17:14]

Optional nit: It might be cleaner to pass the label as a string, and write

std::string name = "Storage.BytesWritten." + label;

[michaeln, 2017/05/19 01:22:05]

i'd rather not have to construct a string at each callsite, i've cleaned it up a
little for readability

void RecordBytesRead(const char* label, int amount) {
  const std::string name = "Storage.BytesRead.";
  base::UmaHistogramCounts10M(name + label, amount);
}

+  GetBytesCountHistogram(name)->Add(amount);
+}
+
+void RecordBytesRead(const char* label, int amount) {
+  std::string name("Storage.BytesRead.");
+  name.append(label);
+  GetBytesCountHistogram(name)->Add(amount);
+}
+
+}  // namespace storage