[Sync] Create UserEventSyncBridge.

components/sync/model/recording_model_type_change_processor.cc

Index: components/sync/model/recording_model_type_change_processor.cc
diff --git a/components/sync/model/recording_model_type_change_processor.cc b/components/sync/model/recording_model_type_change_processor.cc
index 0d379747de9e855cecb81cc841c8de0dd28c7620..e74e44f451aa1fe9cf4b0ee4af8e3457d3e77ece 100644
--- a/components/sync/model/recording_model_type_change_processor.cc
+++ b/components/sync/model/recording_model_type_change_processor.cc
@@ -6,10 +6,27 @@
 
 #include <utility>
 
+#include "base/bind.h"
+#include "base/memory/ptr_util.h"
 #include "components/sync/model/metadata_batch.h"
 
 namespace syncer {
 
+namespace {
+
+std::unique_ptr<ModelTypeChangeProcessor> CreateAndAssignProcessor(
+    RecordingModelTypeChangeProcessor** processor_address,
+    ModelType type,
+    ModelTypeSyncBridge* bridge) {
+  auto processor = base::MakeUnique<RecordingModelTypeChangeProcessor>();
+  *processor_address = processor.get();
+  // Not all compilers are smart enough to up cast during copy elision, so we
+  // explicitly create a correctly typed unique_ptr.
+  return base::WrapUnique(processor.release());
+}
+
+}  // namespace
+
 RecordingModelTypeChangeProcessor::RecordingModelTypeChangeProcessor() {}
 
 RecordingModelTypeChangeProcessor::~RecordingModelTypeChangeProcessor() {}
@@ -41,4 +58,12 @@ void RecordingModelTypeChangeProcessor::SetIsTrackingMetadata(
   is_tracking_metadata_ = is_tracking;
 }
 
+// static
+ModelTypeSyncBridge::ChangeProcessorFactory
+RecordingModelTypeChangeProcessor::FactoryForBridgeTest(
+    RecordingModelTypeChangeProcessor** processor_address) {
+  return base::Bind(&CreateAndAssignProcessor,
+                    base::Unretained(processor_address));
+}
+
 }  //  namespace syncer