Make UMA_HISTOGRAM_ENUMERATION work with scoped enums.

chrome/browser/chromeos/login/screens/user_image_screen.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/chromeos/login/screens/user_image_screen.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 128 matching lines @@
       break;
     default:
       DCHECK(selected_image_ >= 0 &&
              selected_image_ < default_user_image::kDefaultImagesCount);
       image_manager->SaveUserDefaultImageIndex(selected_image_);
       uma_index =
           default_user_image::GetDefaultImageHistogramValue(selected_image_);
       break;
   }
   if (user_has_selected_image_) {
-    UMA_HISTOGRAM_ENUMERATION("UserImage.FirstTimeChoice", uma_index,
-                              default_user_image::kHistogramImagesCount);
+    UMA_HISTOGRAM_EXACT_LINEAR("UserImage.FirstTimeChoice", uma_index,

[wychen, 2017/03/27 20:08:56]

If these constants are converted to enum, uma_index can be converted to enum as
well, and then we can keep using UMA_HISTOGRAM_ENUMERATION.

+                               default_user_image::kHistogramImagesCount);
   }
   ExitScreen();
 }
 
 void UserImageScreen::OnViewDestroyed(UserImageView* view) {
   if (view_ == view)
     view_ = nullptr;
 }
 
 void UserImageScreen::Show() {
@@ skipping 171 matching lines @@
 
 void UserImageScreen::ReportSyncResult(SyncResult timed_out) const {
   base::TimeDelta duration = base::Time::Now() - sync_waiting_start_time_;
   UMA_HISTOGRAM_TIMES("Login.NewUserPriorityPrefsSyncTime", duration);
   UMA_HISTOGRAM_ENUMERATION("Login.NewUserPriorityPrefsSyncResult",
                             static_cast<int>(timed_out),
                             static_cast<int>(SyncResult::COUNT));
 }
 
 }  // namespace chromeos