[Sync] Implement EstimateMemoryUsage for SharedModelTypeProcessor and ModelTypeWorker

components/sync/engine/non_blocking_sync_common.h

Index: components/sync/engine/non_blocking_sync_common.h
diff --git a/components/sync/engine/non_blocking_sync_common.h b/components/sync/engine/non_blocking_sync_common.h
index ef4a8bd3a197695c1d36a6ce3bc2fded22a80513..03b362534f94d5f233902a3ea4742c10ae486547 100644
--- a/components/sync/engine/non_blocking_sync_common.h
+++ b/components/sync/engine/non_blocking_sync_common.h
@@ -60,6 +60,10 @@ using CommitRequestDataList = std::vector<CommitRequestData>;
 using CommitResponseDataList = std::vector<CommitResponseData>;
 using UpdateResponseDataList = std::vector<UpdateResponseData>;
 
+// Returns the estimate of dynamically allocated memory in bytes.
+size_t EstimateMemoryUsage(const CommitRequestData& value);
+size_t EstimateMemoryUsage(const UpdateResponseData& value);
+
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_NON_BLOCKING_SYNC_COMMON_H_