Revert of This CL replaces user_manager::UserID with AccountId.

components/user_manager/user_info.h

Index: components/user_manager/user_info.h
diff --git a/components/user_manager/user_info.h b/components/user_manager/user_info.h
index 2f0cf19ee42bb22951723b800eb64cb5ee8d0818..cc613c188eb1b5ce25215e73532a99cbd51f95e0 100644
--- a/components/user_manager/user_info.h
+++ b/components/user_manager/user_info.h
@@ -8,9 +8,8 @@
 #include <string>
 
 #include "base/strings/string16.h"
+#include "components/user_manager/user_id.h"
 #include "components/user_manager/user_manager_export.h"
-
-class AccountId;
 
 namespace gfx {
 class ImageSkia;
@@ -35,8 +34,9 @@
   // as well as capitalized letters. For example: "Foo.Bar@mock.com".
   virtual std::string GetEmail() const = 0;
 
-  // Returns AccountId for the user.
-  virtual AccountId GetAccountId() const = 0;
+  // Gets the user id (sanitized email address) for the user.
+  // The function would return something like "foobar@mock.com".
+  virtual UserID GetUserID() const = 0;
 
   // Gets the avatar image for the user.
   virtual const gfx::ImageSkia& GetImage() const = 0;