[Sync] Move conflict resolution test code to FakeModelTypeService.

components/sync/api/fake_model_type_service.h

Index: components/sync/api/fake_model_type_service.h
diff --git a/components/sync/api/fake_model_type_service.h b/components/sync/api/fake_model_type_service.h
index 8924601e3331737843c78d6e51721b2a5614841b..9153d3418e50e95dfc6014245cf62a4a0a75913d 100644
--- a/components/sync/api/fake_model_type_service.h
+++ b/components/sync/api/fake_model_type_service.h
@@ -112,6 +112,13 @@ class FakeModelTypeService : public ModelTypeService {
   std::string GetClientTag(const EntityData& entity_data) override;
   std::string GetStorageKey(const EntityData& entity_data) override;
   void OnChangeProcessorSet() override;
+  ConflictResolution ResolveConflict(
+      const EntityData& local_data,
+      const EntityData& remote_data) const override;
+
+  // Store a resolution for the next call to ResolveConflict. Note that if this
+  // is a USE_NEW resolution, the data will only exist for one resolve call.
+  void SetConflictResolution(ConflictResolution resolution);
 
   // Sets the error that the next fallible call to the service will generate.
   void SetServiceError(syncer::SyncError::ErrorType error_type);
@@ -129,6 +136,9 @@ class FakeModelTypeService : public ModelTypeService {
   // Applies |change_list| to the metadata store.
   void ApplyMetadataChangeList(std::unique_ptr<MetadataChangeList> change_list);
 
+  // The conflict resolution to use for calls to ResolveConflict.
+  std::unique_ptr<ConflictResolution> conflict_resolution_;
+
   // The error to produce on the next service call.
   syncer::SyncError service_error_;
 };