[Sync] Migrate bridge implementations to change list based MergeSyncData

components/reading_list/core/reading_list_store.cc

Index: components/reading_list/core/reading_list_store.cc
diff --git a/components/reading_list/core/reading_list_store.cc b/components/reading_list/core/reading_list_store.cc
index 8d0f35590d18189661eabd78625bd71c3154709a..015c7c3ac16312d64a7b66aefcfca1b98898e96a 100644
--- a/components/reading_list/core/reading_list_store.cc
+++ b/components/reading_list/core/reading_list_store.cc
@@ -195,19 +195,18 @@ ReadingListStore::CreateMetadataChangeList() {
 // Perform the initial merge between local and sync data. This should only be
 // called when a data type is first enabled to start syncing, and there is no
 // sync metadata. Best effort should be made to match local and sync data. The
-// keys in the |entity_data_map| will have been created via GetClientTag(...),
-// and if a local and sync data should match/merge but disagree on tags, the
-// service should use the sync data's tag. Any local pieces of data that are
-// not present in sync should immediately be Put(...) to the processor before
-// returning. The same MetadataChangeList that was passed into this function
-// can be passed to Put(...) calls. Delete(...) can also be called but should
-// not be needed for most model types. Durable storage writes, if not able to
-// combine all change atomically, should save the metadata after the data
-// changes, so that this merge will be re-driven by sync if is not completely
-// saved during the current run.
+// storage keys in the |entity_data| are populated with GetStorageKey(...),
+// local and sync copies of the same entity should resolve to the same storage
+// key. Any local pieces of data that are not present in sync should immediately
+// be Put(...) to the processor before returning. The same MetadataChangeList
+// that was passed into this function can be passed to Put(...) calls.
+// Delete(...) can also be called but should not be needed for most model types.
+// Durable storage writes, if not able to combine all change atomically, should
+// save the metadata after the data changes, so that this merge will be re-
+// driven by sync if is not completely saved during the current run.
 base::Optional<syncer::ModelError> ReadingListStore::MergeSyncData(
     std::unique_ptr<syncer::MetadataChangeList> metadata_change_list,
-    syncer::EntityDataMap entity_data_map) {
+    syncer::EntityChangeList entity_data) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   auto token = EnsureBatchCreated();
   // Keep track of the last update of each item.
@@ -216,10 +215,10 @@ base::Optional<syncer::ModelError> ReadingListStore::MergeSyncData(
       model_batch_updates = model_->BeginBatchUpdates();
 
   // Merge sync to local data.
-  for (const auto& kv : entity_data_map) {
-    synced_entries.insert(kv.first);
+  for (const auto& change : entity_data) {
+    synced_entries.insert(change.storage_key());
     const sync_pb::ReadingListSpecifics& specifics =
-        kv.second.value().specifics.reading_list();
+        change.data().specifics.reading_list();
     // Deserialize entry.
     std::unique_ptr<ReadingListEntry> entry(
         ReadingListEntry::FromReadingListSpecifics(specifics, clock_->Now()));