Check node references during sync DB init

chrome/browser/sync/syncable/syncable_id.h

Index: chrome/browser/sync/syncable/syncable_id.h
diff --git a/chrome/browser/sync/syncable/syncable_id.h b/chrome/browser/sync/syncable/syncable_id.h
index 2267040cbcaabbe700949fe928502f9df90164ae..73eb934cb89e74dd5bbf3c1ee43fef40a966a381 100644
--- a/chrome/browser/sync/syncable/syncable_id.h
+++ b/chrome/browser/sync/syncable/syncable_id.h
@@ -87,6 +87,11 @@ class Id {
   inline bool operator > (const Id& that) const {
     return s_ > that.s_;
   }
+
+  const std::string& value() const {
+    return s_;
+  }
+
   // Return the next highest ID in the lexicographic ordering.  This is
   // useful for computing upper bounds on std::sets that are ordered
   // by operator<.