ChromeOS cryptohome should be able to use gaia id as user identifier.

components/signin/core/account_id/account_id.cc

Index: components/signin/core/account_id/account_id.cc
diff --git a/components/signin/core/account_id/account_id.cc b/components/signin/core/account_id/account_id.cc
index 09e5cdf7081212a20e795e580f3c10962f064090..744a1908187e8fc0e68870400dd07895b95681fd 100644
--- a/components/signin/core/account_id/account_id.cc
+++ b/components/signin/core/account_id/account_id.cc
@@ -9,6 +9,7 @@
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/memory/singleton.h"
+#include "base/strings/string_util.h"
 #include "base/values.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 
@@ -49,6 +50,9 @@ AccountId::AccountId() {}
 
 AccountId::AccountId(const std::string& gaia_id, const std::string& user_email)
     : gaia_id_(gaia_id), user_email_(user_email) {
+  CHECK(!base::StartsWith(user_email, "g:", base::CompareCase::SENSITIVE))

[xiyuan, 2016/02/17 23:14:26]

nit: LOG_IF(FATAL, ...) or LOG_ASSERT(...)

Otherwise, the output log lines would not show up in chrome log.

[Alexander Alekseev, 2016/02/18 13:45:15]

Done.

+      << "Bad e-mail: '" << user_email << "' with gaia_id='" << gaia_id << "'";
+
   // TODO(alemate): DCHECK(!email.empty());
   // TODO(alemate): check gaia_id is not empty once it is required.
 }