This CL replaces std::string user_id in ash/* with AccountId.

chrome/browser/ui/views/frame/browser_non_client_frame_view_ash_browsertest.cc

Index: chrome/browser/ui/views/frame/browser_non_client_frame_view_ash_browsertest.cc
diff --git a/chrome/browser/ui/views/frame/browser_non_client_frame_view_ash_browsertest.cc b/chrome/browser/ui/views/frame/browser_non_client_frame_view_ash_browsertest.cc
index ec64e54d12f12f21ad2b01d686ff2a32c70ce936..0c8e4a5f52ea55310617ca431abd1e27545dd7c6 100644
--- a/chrome/browser/ui/views/frame/browser_non_client_frame_view_ash_browsertest.cc
+++ b/chrome/browser/ui/views/frame/browser_non_client_frame_view_ash_browsertest.cc
@@ -28,6 +28,7 @@
 #include "chrome/browser/ui/ash/multi_user/multi_user_util.h"
 #include "chrome/browser/ui/ash/multi_user/multi_user_window_manager_test.h"
 #include "chrome/browser/ui/views/profiles/avatar_menu_button.h"
+#include "components/signin/core/account_id/account_id.h"
 #endif  // defined(OS_CHROMEOS)
 
 using views::Widget;
@@ -225,14 +226,14 @@ IN_PROC_BROWSER_TEST_F(BrowserNonClientFrameViewAshTest,
 
   EXPECT_FALSE(chrome::MultiUserWindowManager::ShouldShowAvatar(window));
 
-  const std::string current_user =
-      multi_user_util::GetUserIDFromProfile(browser()->profile());
+  const AccountId current_account_id =
+      multi_user_util::GetAccountIdFromProfile(browser()->profile());
   TestMultiUserWindowManager* manager =
-      new TestMultiUserWindowManager(browser(), current_user);
+      new TestMultiUserWindowManager(browser(), current_account_id);
 
   // Teleport the window to another desktop.
-  const std::string user2 = "user2";
-  manager->ShowWindowForUser(window, user2);
+  const AccountId account_id2(AccountId::FromUserEmail("user2"));
+  manager->ShowWindowForUser(window, account_id2);
   EXPECT_TRUE(chrome::MultiUserWindowManager::ShouldShowAvatar(window));
 
   // Avatar should show on the top left corner of the teleported browser window.
@@ -253,14 +254,15 @@ IN_PROC_BROWSER_TEST_F(BrowserNonClientFrameViewAshTest,
                            profiles::kAvatarIconHeight / 2);
   EXPECT_EQ(HTCLIENT, frame_view->NonClientHitTest(avatar_center));
 
-  const std::string current_user =
-      multi_user_util::GetUserIDFromProfile(browser()->profile());
+  const AccountId current_user =
+      multi_user_util::GetAccountIdFromProfile(browser()->profile());
   TestMultiUserWindowManager* manager =
       new TestMultiUserWindowManager(browser(), current_user);
 
   // Teleport the window to another desktop.
-  const std::string user2 = "user2";
-  manager->ShowWindowForUser(browser()->window()->GetNativeWindow(), user2);
+  const AccountId account_id2(AccountId::FromUserEmail("user2"));
+  manager->ShowWindowForUser(browser()->window()->GetNativeWindow(),
+                             account_id2);
   // Clicking on the avatar icon should have same behaviour like clicking on
   // the caption area, i.e., allow the user to drag the browser window around.
   EXPECT_EQ(HTCAPTION, frame_view->NonClientHitTest(avatar_center));