Add pretty-printing for PasswordStore::FormDigest

components/password_manager/core/browser/password_store.h

Index: components/password_manager/core/browser/password_store.h
diff --git a/components/password_manager/core/browser/password_store.h b/components/password_manager/core/browser/password_store.h
index 4d5067495ae237d88f409c0505bfc134c11c8479..969e7df05a9b7f5c415cf7eed04ea234528de797 100644
--- a/components/password_manager/core/browser/password_store.h
+++ b/components/password_manager/core/browser/password_store.h
@@ -6,6 +6,7 @@
 #define COMPONENTS_PASSWORD_MANAGER_CORE_BROWSER_PASSWORD_STORE_H_
 
 #include <memory>
+#include <ostream>
 #include <string>
 #include <vector>
 
@@ -493,6 +494,10 @@ class PasswordStore : protected PasswordStoreSync,
   DISALLOW_COPY_AND_ASSIGN(PasswordStore);
 };
 
+// For logging only.
+std::ostream& operator<<(std::ostream& os,
+                         const PasswordStore::FormDigest& digest);
+
 }  // namespace password_manager
 
 #endif  // COMPONENTS_PASSWORD_MANAGER_CORE_BROWSER_PASSWORD_STORE_H_