[Sync] Support commit only types.

components/sync/model_impl/shared_model_type_processor.h

Index: components/sync/model_impl/shared_model_type_processor.h
diff --git a/components/sync/model_impl/shared_model_type_processor.h b/components/sync/model_impl/shared_model_type_processor.h
index d8b54483b8e008cff802ac04bc926c12144941b7..0addb85430887b22c16fb83995381b0e18445bea 100644
--- a/components/sync/model_impl/shared_model_type_processor.h
+++ b/components/sync/model_impl/shared_model_type_processor.h
@@ -40,7 +40,8 @@ class SharedModelTypeProcessor : public ModelTypeProcessor,
  public:
   SharedModelTypeProcessor(ModelType type,
                            ModelTypeSyncBridge* bridge,
-                           const base::RepeatingClosure& dump_stack);
+                           const base::RepeatingClosure& dump_stack,
+                           bool commit_only);
   ~SharedModelTypeProcessor() override;
 
   // Whether the processor is allowing changes to its model type. If this is
@@ -210,6 +211,10 @@ class SharedModelTypeProcessor : public ModelTypeProcessor,
   // client tag hash. The other direction can use |entities_|.
   std::map<std::string, std::string> storage_key_to_tag_hash_;
 
+  // If the processor should behave as if |type_| is one of the commit only
+  // model types.
+  bool commit_only_;
+
   SEQUENCE_CHECKER(sequence_checker_);
 
   // WeakPtrFactory for this processor which will be sent to sync thread.