Add Ash.Wallpaper.{DefaultIndex,Type} to histograms.xml.

components/user_manager/user.h

 // Copyright 2014 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_USER_MANAGER_USER_H_
 #define COMPONENTS_USER_MANAGER_USER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 42 matching lines @@
     USER_IMAGE_INVALID = -3,
 
     // Returned as |image_index| when user profile image is used as user image.
     USER_IMAGE_PROFILE = -2,
 
     // Returned as |image_index| when user-selected file or photo is used as
     // user image.
     USER_IMAGE_EXTERNAL = -1,
   } UserImageType;
 
+  // This enum is used to define the buckets for an enumerated UMA histogram.
+  // Hence,
+  //   (a) existing enumerated constants should never be deleted or reordered,
+  //   (b) new constants should only be appended at the end of the enumeration.
   enum WallpaperType {
-    /* DAILY = 0 */    // Removed.  Do not re-use the id!
+    /* DAILY = 0 */    // Removed.
     CUSTOMIZED = 1,    // Selected by user.
     DEFAULT = 2,       // Default.
-    /* UNKNOWN = 3 */  // Removed.  Do not re-use the id!
-    ONLINE = 4,        // WallpaperInfo.file denotes an URL.
+    /* UNKNOWN = 3 */  // Removed.
+    ONLINE = 4,        // WallpaperInfo.location denotes an URL.
     POLICY = 5,        // Controlled by policy, can't be changed by the user.
     WALLPAPER_TYPE_COUNT = 6
   };
 
   // Returns the user type.
   virtual UserType GetType() const = 0;
 
   // The email the user used to log in.
   const std::string& email() const { return email_; }
 
@@ skipping 184 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(User);
 };
 
 // List of known users.
 typedef std::vector<User*> UserList;
 
 }  // namespace user_manager
 
 #endif  // COMPONENTS_USER_MANAGER_USER_H_