Persist setup metrics and have Chrome report them during UMA upload.

components/metrics/file_metrics_provider.h

+// Copyright 2016 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 COMPONENTS_METRICS_FILE_METRICS_PROVIDER_H_
+#define COMPONENTS_METRICS_FILE_METRICS_PROVIDER_H_
+
+#include <list>
+#include <string>
+
+#include "base/callback.h"
+#include "base/files/file_path.h"
+#include "base/gtest_prod_util.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
+#include "base/time/time.h"
+#include "components/metrics/metrics_provider.h"
+
+class PrefRegistrySimple;
+class PrefService;
+
+namespace base {
+class MemoryMappedFile;
+class PersistentMemoryAllocator;
+}
+
+namespace metrics {
+
+class MetricsService;
+
+// FileMetricsProvider gathers and logs histograms written to files on disk.
+// Any number of files can be registered and the will be polled once per

[grt (UTC plus 2), 2016/02/08 18:09:19]

"and the will be polled"

[bcwhite, 2016/02/09 21:08:46]

Done.

+// upload cycle (at startup and about every 30 minutes thereafter) for data
+// to send.
+class FileMetricsProvider
+    : public metrics::MetricsProvider {
+ public:
+  enum FileType {
+    // "Atomic" files are a collection of histograms that are written
+    // completely in a single atomic operation (typically a write followed
+    // by an atomic rename) and the file is never updated again except to
+    // be replaced by a completely new set of histograms. This is the only
+    // option that can be used if the file is not writeable by *this*
+    // process.
+    FILE_HISTOGRAMS_ATOMIC,
+
+    // "Active" files may be open by one or more other processes and updated
+    // at any time with new samples or new histograms. Such files may also be
+    // inactive for any period of time only to be opened again and have new
+    // data written to it. Because the file will be actively watched by *this*

[grt (UTC plus 2), 2016/02/08 18:09:19]

nit: it -> them since the subject is "Such files"

[bcwhite, 2016/02/09 21:08:46]

Done.

+    // process, the underlying file cannot be deleted on operating systems
+    // that do not support delete-while-open (e.g. Windows).

[grt (UTC plus 2), 2016/02/08 18:09:19]

Windows does, sorta. If all openers use FLAG_SHARE_DELETE when opening the file,
then any opener can also use FLAG_DELETE_ON_CLOSE to trigger the file's
evaporation once it's no longer in use.

[grt (UTC plus 2), 2016/02/15 15:42:39]

Please update the comment here, as Windows does support delete-while-open.

[bcwhite, 2016/02/15 19:22:10]

Done, but differently since on reflection, the file should probably not be
deleted anyway.

+    // TODO(bcwhite): Enable when read/write mem-mapped files are supported.
+    //FILE_HISTOGRAMS_ACTIVE,
+  };
+
+ private:
+  // This is fully defined in the header file (rather than just a forward
+  // declaration) so it can be known to tests.
+  struct FileInformation {
+    FileInformation();
+    ~FileInformation();
+
+    base::FilePath path;
+    FileType type;
+    std::string prefs_key;
+    base::Time last_seen;
+    scoped_ptr<base::MemoryMappedFile> mapped;
+    scoped_ptr<base::PersistentMemoryAllocator> allocator;
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(FileInformation);
+  };
+
+ public:
+  typedef std::list<scoped_ptr<FileInformation>> FileInformationList;
+
+  FileMetricsProvider(metrics::MetricsService* metrics_service,
+                      PrefService* local_state);
+  ~FileMetricsProvider() override;
+
+  // Indicate a file to be monitored and how the file is used. Because some
+  // metadata must persist across process restarts, registry entries are used

[grt (UTC plus 2), 2016/02/08 18:09:19]

regarding "registry entries", do you mean "preference values"? AFAICT, the
Windows registry isn't used.

[bcwhite, 2016/02/09 21:08:46]

Done.  Was thinking in terms of "PrefRegistry".

+  // based on the |prefs_key| name. Call RegisterPrefs() with the same name
+  // to create the necessary keys in advance.
+  void RegisterFile(const base::FilePath& path, FileType type,
+                    const base::StringPiece& prefs_key);
+
+  static void RegisterPrefs(PrefRegistrySimple* prefs,
+                            const base::StringPiece& key);
+
+ private:
+  friend class FileMetricsProviderTest;
+  FRIEND_TEST_ALL_PREFIXES(FileMetricsProviderTest, AccessMetrics);
+
+  static void CheckAndMapNewMetricFilesOnBlockingPool(
+      FileInformationList* files,
+      base::Callback<void(FileInformationList*)> callback);
+  static bool CheckAndMapNewMetrics(FileInformation* file);
+
+  void ScheduleFilesCheck();
+  void RecordFileInformation(FileInformationList* files);
+  void RecordFileAsSeen(FileInformation* file);
+
+  // metrics::MetricsDataProvider:
+  void OnDidCreateMetricsLog() override;
+  void RecordHistogramSnapshots(base::HistogramSnapshotManager* hsm) override;
+
+  base::Lock lock_;
+  FileInformationList metrics_files_;
+  FileInformationList metrics_found_;
+  metrics::MetricsService* metrics_service_;
+  PrefService* pref_service_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileMetricsProvider);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_FILE_METRICS_PROVIDER_H_