Overload << operator to allow logging of AccountIds.

components/signin/core/account_id/account_id.h

Index: components/signin/core/account_id/account_id.h
diff --git a/components/signin/core/account_id/account_id.h b/components/signin/core/account_id/account_id.h
index 81082b5fe0445252c4c272afde8c676e33e7b5dd..a263178d13d7a2bc41914679d9183c09bb96adce 100644
--- a/components/signin/core/account_id/account_id.h
+++ b/components/signin/core/account_id/account_id.h
@@ -7,7 +7,9 @@
 
 #include <stddef.h>
 
+#include <ostream>
 #include <string>
+
 #include "base/containers/hash_tables.h"
 
 enum class AccountType { UNKNOWN, GOOGLE, ACTIVE_DIRECTORY };
@@ -97,6 +99,8 @@ class AccountId {
                           AccountId* out_account_id);
 
  private:
+  friend std::ostream& operator<<(std::ostream&, const AccountId&);
+
   AccountId(const std::string& id,
             const std::string& user_email,
             const AccountType& account_type);
@@ -106,6 +110,9 @@ class AccountId {
   AccountType account_type_ = AccountType::UNKNOWN;
 };
 
+// Overload << operator to allow logging of AccountIds.
+std::ostream& operator<<(std::ostream& stream, const AccountId& account_id);
+
 // Returns a reference to a singleton.
 const AccountId& EmptyAccountId();