We should use UserID object to identify users instead of username.

chrome/browser/ui/webui/options/chromeos/user_image_source.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/ui/webui/options/chromeos/user_image_source.h"
 
 #include "base/memory/ref_counted_memory.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string_split.h"
 #include "chrome/common/url_constants.h"
+#include "components/user_manager/user_id.h"
 #include "components/user_manager/user_image/default_user_images.h"
 #include "components/user_manager/user_manager.h"
 #include "grit/theme_resources.h"
 #include "grit/ui_chromeos_resources.h"
 #include "net/base/escape.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/codec/png_codec.h"
 #include "url/url_parse.h"
 
 namespace {
 
 // Parses the user image URL, which looks like
 // "chrome://userimage/user@host?key1=value1&...&key_n=value_n",
 // to user email.
 void ParseRequest(const GURL& url,
                   std::string* email) {
   DCHECK(url.is_valid());
   *email = net::UnescapeURLComponent(url.path().substr(1),
                                     (net::UnescapeRule::URL_SPECIAL_CHARS |
                                      net::UnescapeRule::SPACES));
 }
 
 }  // namespace
 
 namespace chromeos {
 namespace options {
 
 // Static.
 base::RefCountedMemory* UserImageSource::GetUserImage(
-    const std::string& email,
+    const user_manager::UserID& user_id,
     ui::ScaleFactor scale_factor) {
   const user_manager::User* user =
-      user_manager::UserManager::Get()->FindUser(email);
+      user_manager::UserManager::Get()->FindUser(user_id);
   if (user) {
     if (user->has_raw_image()) {
       return new base::RefCountedBytes(user->raw_image());
     } else if (user->image_is_stub()) {
       return ResourceBundle::GetSharedInstance().
           LoadDataResourceBytesForScale(IDR_PROFILE_PICTURE_LOADING,
                                         scale_factor);
     } else if (user->HasDefaultImage()) {
       return ResourceBundle::GetSharedInstance().
           LoadDataResourceBytesForScale(
@@ skipping 17 matching lines @@
 }
 
 void UserImageSource::StartDataRequest(
     const std::string& path,
     int render_process_id,
     int render_frame_id,
     const content::URLDataSource::GotDataCallback& callback) {
   std::string email;
   GURL url(chrome::kChromeUIUserImageURL + path);
   ParseRequest(url, &email);
-  callback.Run(GetUserImage(email, ui::SCALE_FACTOR_100P));
+  callback.Run(GetUserImage(user_manager::UserID::FromUserEmail(email), ui::SCALE_FACTOR_100P));
 }
 
 std::string UserImageSource::GetMimeType(const std::string& path) const {
   // We need to explicitly return a mime type, otherwise if the user tries to
   // drag the image they get no extension.
   return "image/png";
 }
 
 }  // namespace options
 }  // namespace chromeos