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

chrome/browser/extensions/extension_assets_manager_chromeos.cc

Index: chrome/browser/extensions/extension_assets_manager_chromeos.cc
diff --git a/chrome/browser/extensions/extension_assets_manager_chromeos.cc b/chrome/browser/extensions/extension_assets_manager_chromeos.cc
index 3daea4e4a8e59fed213565965e103fd138fb59fc..acdb280d5fe8fa3ac056529254f1bb53e6fa7c2c 100644
--- a/chrome/browser/extensions/extension_assets_manager_chromeos.cc
+++ b/chrome/browser/extensions/extension_assets_manager_chromeos.cc
@@ -280,14 +280,14 @@ void ExtensionAssetsManagerChromeOS::CheckSharedExtension(
     InstallExtensionCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  const std::string& user_id = profile->GetProfileUserName();
+  const user_manager::User* user = chromeos::ProfileHelper::Get()->GetUserByProfile(profile);
   user_manager::UserManager* user_manager = user_manager::UserManager::Get();
   if (!user_manager) {
     NOTREACHED();
     return;
   }
 
-  if (user_manager->IsUserNonCryptohomeDataEphemeral(user_id) ||
+  if (user_manager->IsUserNonCryptohomeDataEphemeral(user->GetUserID()) ||
       !user_manager->IsLoggedInAsUserWithGaiaAccount()) {
     // Don't cache anything in shared location for ephemeral user or special
     // user types.
@@ -318,14 +318,14 @@ void ExtensionAssetsManagerChromeOS::CheckSharedExtension(
     bool user_found = false;
     for (size_t i = 0; i < users_size; i++) {
       std::string temp;
-      if (users->GetString(i, &temp) && temp == user_id) {
+      if (users->GetString(i, &temp) && temp == user->GetUserID().GetUserEmail()) {
         // Re-installation for the same user.
         user_found = true;
         break;
       }
     }
     if (!user_found)
-      users->AppendString(user_id);
+      users->AppendString(user->GetUserID().GetUserEmail());
 
     // unpacked_extension_root will be deleted by CrxInstaller.
     ExtensionAssetsManagerChromeOS::GetFileTaskRunner(profile)->PostTask(
@@ -525,11 +525,12 @@ bool ExtensionAssetsManagerChromeOS::CleanUpExtension(
 
     size_t num_users = users->GetSize();
     for (size_t i = 0; i < num_users; i++) {
-      std::string user_id;
-      if (!users->GetString(i, &user_id)) {
+      std::string user_email;
+      if (!users->GetString(i, &user_email)) {
         NOTREACHED();
         return false;
       }
+      const user_manager::UserID user_id(std::string() /* gaia_id */, user_email);
       const user_manager::User* user = user_manager->FindUser(user_id);
       bool not_used = false;
       if (!user) {