UMA stats for MTP file system in Chrome OS Files.app.

chrome/browser/chromeos/file_manager/volume_manager.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_FILE_MANAGER_VOLUME_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_FILE_MANAGER_VOLUME_MANAGER_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 22 matching lines @@
 
 namespace content {
 class BrowserContext;
 }  // namespace content
 
 namespace file_manager {
 
 class MountedDiskMonitor;
 class VolumeManagerObserver;
 
-// This manager manages "Drive" and "Downloads" in addition to disks managed
-// by DiskMountManager.
+// Identifiers for volume types managed by Chrome OS file manager.
+// The list must be kept in sync with FileManagerVolumeType enum
+// in tools/metrics/histograms/histograms.xml for recording user metric.
 enum VolumeType {
   VOLUME_TYPE_GOOGLE_DRIVE,
   VOLUME_TYPE_DOWNLOADS_DIRECTORY,
   VOLUME_TYPE_REMOVABLE_DISK_PARTITION,
   VOLUME_TYPE_MOUNTED_ARCHIVE_FILE,
   VOLUME_TYPE_CLOUD_DEVICE,
   VOLUME_TYPE_PROVIDED,  // File system provided by the FileSystemProvider API.
   VOLUME_TYPE_MTP,
-  VOLUME_TYPE_TESTING
+  VOLUME_TYPE_TESTING,  // Used only in tests.

[Ilya Sherman, 2014/05/08 21:16:11]

nit: Since enums used for histograms should be append-only, I'd recommend making
this be the first item in the enum rather than the last.  That way, you don't
end up with gaps in terms of which items are relevant for histograms.xml.

(I'd also add a quick comment to document that this enum should be treated as
append-only.)

[kinaba, 2014/05/09 02:09:27]

Thanks for the suggestion. Done.

+  NUM_VOLUME_TYPE,
 };
 
 struct VolumeInfo {
   VolumeInfo();
   ~VolumeInfo();
 
   // The ID for provided file system. If other type, then equal to zero.
   int file_system_id;
 
   // The ID of the volume.
@@ skipping 151 matching lines @@
 
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<VolumeManager> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(VolumeManager);
 };
 
 }  // namespace file_manager
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILE_MANAGER_VOLUME_MANAGER_H_