[Sync] Implement EstimateMemoryUsage for SharedModelTypeProcessor and ModelTypeWorker

components/sync/model/entity_data.h

Index: components/sync/model/entity_data.h
diff --git a/components/sync/model/entity_data.h b/components/sync/model/entity_data.h
index ee7e18f298cbadee76748f18e31f9f3224107f84..25c2bbe426e81d3ab57c54a46074a215fb37e7cd 100644
--- a/components/sync/model/entity_data.h
+++ b/components/sync/model/entity_data.h
@@ -79,6 +79,9 @@ struct EntityData {
   // Dumps all info into a DictionaryValue and returns it.
   std::unique_ptr<base::DictionaryValue> ToDictionaryValue();
 
+  // Returns the estimate of dynamically allocated memory in bytes.
+  size_t EstimateMemoryUsage() const;
+
  private:
   friend struct EntityDataTraits;
   // Used to transfer the data without copying.