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.
 enum VolumeType {
-  VOLUME_TYPE_GOOGLE_DRIVE,
+  VOLUME_TYPE_TESTING = -1,  // Used only in tests.
+  VOLUME_TYPE_GOOGLE_DRIVE = 0,
   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
+  // The enum values must be kept in sync with FileManagerVolumeType in
+  // tools/metrics/histograms/histograms.xml. Since enums for histograms are
+  // append-only (for keeping the number consistent across versions), new values
+  // for this enum also has to be always appended at the end (i.e., here).
+  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_