sync: Implement per-type commit interface

sync/sync_tests.gypi

Index: sync/sync_tests.gypi
diff --git a/sync/sync_tests.gypi b/sync/sync_tests.gypi
index 93d6ed8f753e602169fb6be75305889a70706f94..afd41fec47d8cfcfba8703f938e310c0b0c5e703 100644
--- a/sync/sync_tests.gypi
+++ b/sync/sync_tests.gypi
@@ -239,12 +239,12 @@
           'engine/backoff_delay_provider_unittest.cc',
           'engine/download_unittest.cc',
           'engine/model_changing_syncer_command_unittest.cc',
-          'engine/process_commit_response_command_unittest.cc',
           'engine/process_updates_command_unittest.cc',
           'engine/store_timestamps_command_unittest.cc',
           'engine/sync_scheduler_unittest.cc',
           'engine/syncer_proto_util_unittest.cc',
           'engine/syncer_unittest.cc',
+          'engine/sync_directory_commit_contribution_unittest.cc',
           'engine/traffic_recorder_unittest.cc',
           'js/js_arg_list_unittest.cc',
           'js/js_event_details_unittest.cc',
@@ -252,7 +252,6 @@
           'protocol/proto_enum_conversions_unittest.cc',
           'protocol/proto_value_conversions_unittest.cc',
           'sessions/nudge_tracker_unittest.cc',
-          'sessions/ordered_commit_set_unittest.cc',
           'sessions/status_controller_unittest.cc',
           'sessions/sync_session_unittest.cc',
           'syncable/directory_backing_store_unittest.cc',