This CL replaces e-mail with AccountId on user selection screen.

components/login/base_screen_handler_utils.h

Index: components/login/base_screen_handler_utils.h
diff --git a/components/login/base_screen_handler_utils.h b/components/login/base_screen_handler_utils.h
index 71d2e7f1687ff6417d0dd839878532f017694c7a..7d884d2d42996a5072d974b6f7b37df173c4c0cd 100644
--- a/components/login/base_screen_handler_utils.h
+++ b/components/login/base_screen_handler_utils.h
@@ -14,6 +14,7 @@
 #include "base/tuple.h"
 #include "base/values.h"
 #include "components/login/login_export.h"
+#include "components/signin/core/account_id/account_id.h"
 
 namespace login {
 
@@ -40,6 +41,7 @@ bool LOGIN_EXPORT ParseValue(const base::Value* value,
                              const base::DictionaryValue** out_value);
 bool LOGIN_EXPORT ParseValue(const base::Value* value, StringList* out_value);
 bool LOGIN_EXPORT ParseValue(const base::Value* value, String16List* out_value);
+bool LOGIN_EXPORT ParseValue(const base::Value* value, AccountId* out_value);
 
 template <typename T>
 inline bool GetArg(const base::ListValue* args, size_t index, T* out_value) {
@@ -54,17 +56,29 @@ base::FundamentalValue LOGIN_EXPORT MakeValue(int v);
 base::FundamentalValue LOGIN_EXPORT MakeValue(double v);
 base::StringValue LOGIN_EXPORT MakeValue(const std::string& v);
 base::StringValue LOGIN_EXPORT MakeValue(const base::string16& v);
+base::StringValue LOGIN_EXPORT MakeValue(const AccountId& v);
 
 template <typename T>
 inline const T& MakeValue(const T& v) {
   return v;
 }
 
+template <typename T>
+struct ParsedValueContainer {
+  T value;
+};
+
+template <>
+struct LOGIN_EXPORT ParsedValueContainer<AccountId> {
+  ParsedValueContainer();
+  AccountId value = EmptyAccountId();
+};
+
 template <typename Arg, size_t index>
 typename UnwrapConstRef<Arg>::Type ParseArg(const base::ListValue* args) {
-  typename UnwrapConstRef<Arg>::Type parsed;
-  CHECK(GetArg(args, index, &parsed));
-  return parsed;
+  ParsedValueContainer<typename UnwrapConstRef<Arg>::Type> parsed;
+  CHECK(GetArg(args, index, &parsed.value));
+  return parsed.value;
 }
 
 template <typename... Args, size_t... Ns>