[Password Manager] Add UMA stats to track interaction with synced accounts.

components/password_manager/core/browser/login_database.h

Index: components/password_manager/core/browser/login_database.h
diff --git a/components/password_manager/core/browser/login_database.h b/components/password_manager/core/browser/login_database.h
index b3b09389219eac0e8298fcaa08fc5ae242c02858..9c9f2732a5a12b4d936964f3156e682da55283e0 100644
--- a/components/password_manager/core/browser/login_database.h
+++ b/components/password_manager/core/browser/login_database.h
@@ -31,7 +31,7 @@ class LoginDatabase {
   bool Init(const base::FilePath& db_path);
 
   // Reports usage metrics to UMA.
-  void ReportMetrics();
+  void ReportMetrics(const std::string& sync_username);
 
   // Adds |form| to the list of remembered password forms. Returns the list of
   // changes applied ({}, {ADD}, {REMOVE, ADD}). If it returns {REMOVE, ADD}