Move memory histograms generation to MetricsMemoryDetails.

chrome/browser/metrics/metrics_memory_details.h

+// Copyright 2015 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.
+
+#ifndef CHROME_BROWSER_METRICS_METRICS_MEMORY_DETAILS_H_
+#define CHROME_BROWSER_METRICS_METRICS_MEMORY_DETAILS_H_
+
+#include <map>
+
+#include "base/callback.h"
+#include "chrome/browser/memory_details.h"
+
+// MemoryGrowthTracker tracks latest metrics about record time and memory usage
+// at that time per process.
+class MemoryGrowthTracker {
+ public:
+  MemoryGrowthTracker();
+  ~MemoryGrowthTracker();
+
+  // If 30 minutes have passed since last UMA record, UpdateSample() computes

[Ilya Sherman, 2015/01/16 04:57:36]

Why 30 minutes?  Is it too expensive to compute once per UMA upload?

[Alexei Svitkine (slow), 2015/01/16 16:07:50]

I'm not changing this - this is just moving from the other file.

This class is a helper to support the Memory.RendererShrinkIn30Min and
Memory.RendererGrowthIn30Min histograms.

+  // a difference between current memory usage |sample| of process |pid| and
+  // stored memory usage at the time of last UMA record. Then, it updates the
+  // stored memory usage to |sample|, stores the difference in |diff| and
+  // returns true.
+  // If no memory usage of |pid| has not been recorded so far or 30 minutes
+  // have not passed since last record, it just returns false.
+  // |sample| is memory usage in kB.
+  bool UpdateSample(base::ProcessId pid, int sample, int* diff);
+
+ private:
+  // Latest metrics about record time and memory usage at that time per process.
+  // The second values of |memory_sizes_| are in kB.
+  std::map<base::ProcessId, base::TimeTicks> times_;
+  std::map<base::ProcessId, int> memory_sizes_;
+
+  DISALLOW_COPY_AND_ASSIGN(MemoryGrowthTracker);
+};
+
+// Handles asynchronous fetching of memory details.
+// Will run the provided task after finished.
+class MetricsMemoryDetails : public MemoryDetails {
+ public:
+  MetricsMemoryDetails(const base::Closure& callback,
+                       MemoryGrowthTracker* memory_growth_tracker);
+
+ protected:
+  ~MetricsMemoryDetails() override;
+
+  // MemoryDetails:
+  void OnDetailsAvailable() override;
+
+ private:
+  // Updates the global histograms for tracking memory usage.
+  void UpdateHistograms();
+
+#if defined(OS_CHROMEOS)
+  void UpdateSwapHistograms();
+#endif
+
+  base::Closure callback_;
+
+  // A pointer to MemoryGrowthTracker which is contained in a longer-lived
+  // owner of MemoryDetails, for example, ChromeMetricsServiceClient.
+  // The pointer is NULL by default and set by SetMemoryGrowthTracker().
+  // If it is NULL, nothing is tracked.

[Ilya Sherman, 2015/01/16 04:57:36]

Please update this comment -- there's no longer a SetMemoryGrowthTracker()
method.

[Alexei Svitkine (slow), 2015/01/16 16:07:50]

Done.

+  MemoryGrowthTracker* memory_growth_tracker_;
+
+  DISALLOW_COPY_AND_ASSIGN(MetricsMemoryDetails);
+};
+
+#endif  // CHROME_BROWSER_METRICS_METRICS_MEMORY_DETAILS_H_