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/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
+#include "base/time/time.h"
+#include "components/metrics/metrics_provider.h"
+
+class PrefRegistrySimple;
+class PrefService;
+
+namespace base {
+class MemoryMappedFile;
+class PersistentMemoryAllocator;
+class TaskRunner;
+}
+
+namespace metrics {
+
+// FileMetricsProvider gathers and logs histograms written to files on disk.
+// Any number of files can be registered and will be polled once per upload
+// cycle (at startup and about every 30 minutes thereafter) for data to send.

[Alexei Svitkine (slow), 2016/02/19 18:16:40]

The 30 minutes is a desktop-specific interval. Please rephrase the comment to
either mention this as an example "e.g. 30 minutes on desktop" or just not
mention the specific interval.

[bcwhite, 2016/02/19 19:50:15]

Done.

+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 them. The file should probably never be deleted because
+    // there would be no guarantee that the data has been reported.
+    // TODO(bcwhite): Enable when read/write mem-mapped files are supported.
+    //FILE_HISTOGRAMS_ACTIVE,
+  };
+
+  FileMetricsProvider(const scoped_refptr<base::TaskRunner>& task_runner,
+                      PrefService* local_state);
+  ~FileMetricsProvider() override;
+
+  // Indicate a file to be monitored and how the file is used. Because some

[Alexei Svitkine (slow), 2016/02/19 18:16:40]

Nit: Indicates

[bcwhite, 2016/02/19 19:50:15]

Done.

+  // metadata may persist across process restarts, preferences entries are
+  // used based on the |prefs_key| name. Call RegisterPrefs() with the same
+  // name to create the necessary keys in advance. Set |prefs_key| empty
+  // if no persistence is required.
+  void RegisterFile(const base::FilePath& path, FileType type,

[Alexei Svitkine (slow), 2016/02/19 18:16:40]

Nit: 1 param per line.

[bcwhite, 2016/02/19 19:50:15]

Done.

+                    const base::StringPiece prefs_key);
+
+  // Registers all necessary preferences for maintaining persistent state
+  // about a monitored file across process restarts. The |prefs_key| is
+  // typically the filename.
+  static void RegisterPrefs(PrefRegistrySimple* prefs,
+                            const base::StringPiece prefs_key);
+
+ private:
+  friend class FileMetricsProviderTest;
+  FRIEND_TEST_ALL_PREFIXES(FileMetricsProviderTest, AccessMetrics);
+
+  // The different results that can occur accessing a file.
+  enum AccessResult {
+    // File was successfully mapped.
+    ACCESS_RESULT_SUCCESS,
+
+    // File does not exist.
+    ACCESS_RESULT_DOESNT_EXIST,
+
+    // File exists but not modified since last read.
+    ACCESS_RESULT_NOT_MODIFIED,
+
+    // File is not valid: is a directory or zero-size.
+    ACCESS_RESULT_INVALID_FILE,
+
+    // System could not map file into memory.
+    ACCESS_RESULT_SYSTEM_MAP_FAILURE,
+
+    // File had invalid contents.
+    ACCESS_RESULT_INVALID_CONTENTS,
+
+    ACCESS_RESULT_MAX
+  };
+
+  // Information about files being monitored; defined and used exclusively
+  // inside the .cc file.
+  struct FileInfo;
+  using FileInfoList = std::list<scoped_ptr<FileInfo>>;
+
+  // Checks a list of files (on a task-runner allowed to do I/O) to see if
+  // any should be processed during the next histogram collection.
+  static void CheckAndMapNewMetricFilesOnTaskRunner(FileInfoList* files);
+
+  // Checks an individual file as part of CheckAndMapNewMetricFilesOnTaskRunner.
+  static AccessResult CheckAndMapNewMetrics(FileInfo* file);
+
+  // Creates a task to check all monitored files for updates.
+  void ScheduleFilesCheck();
+
+  // Creates a PersistentMemoryAllocator for a file that has been marked to
+  // have its metrics collected.
+  void CreateAllocatorForFile(FileInfo* file);
+
+  // Records all histograms from a given file via a snapshot-manager.
+  void RecordHistogramSnapshotsFromFile(
+      base::HistogramSnapshotManager* snapshot_manager,
+      FileInfo* file);
+
+  // Takes a list of files checked by an external task and determines what
+  // to do with each.
+  void RecordFilesChecked(FileInfoList* checked);
+
+  // Updates the persistent state information to show a file as being read.
+  void RecordFileAsSeen(FileInfo* file);
+
+  // metrics::MetricsDataProvider:
+  void OnDidCreateMetricsLog() override;
+  void RecordHistogramSnapshots(
+      base::HistogramSnapshotManager* snapshot_manager) override;
+
+  // A task-runner capable of performing I/O.
+  scoped_refptr<base::TaskRunner> task_runner_;
+
+  // A list of files not currently active that need to be checked for changes.
+  FileInfoList files_to_check_;
+
+  // A list of files that have data to be read and reported.
+  FileInfoList files_to_read_;
+
+  // The preferences-service used to store persistent state about files.
+  PrefService* pref_service_;
+
+  base::ThreadChecker thread_checker_;
+  base::WeakPtrFactory<FileMetricsProvider> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileMetricsProvider);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_FILE_METRICS_PROVIDER_H_