sync: Introduce classes for per-type counters

sync/sync_core.gypi

Index: sync/sync_core.gypi
diff --git a/sync/sync_core.gypi b/sync/sync_core.gypi
index e7019a013ff5fc71cc7f00ca1188cebf3280b4c6..5efe9ae3d4b1d3644526b36268d7bcd01bac310d 100644
--- a/sync/sync_core.gypi
+++ b/sync/sync_core.gypi
@@ -35,11 +35,11 @@
     'engine/backoff_delay_provider.cc',
     'engine/backoff_delay_provider.h',
     'engine/commit.cc',
+    'engine/commit.h',
     'engine/commit_contribution.cc',
     'engine/commit_contribution.h',
     'engine/commit_contributor.cc',
     'engine/commit_contributor.h',
-    'engine/commit.h',
     'engine/commit_processor.cc',
     'engine/commit_processor.h',
     'engine/commit_util.cc',
@@ -54,8 +54,6 @@
     'engine/directory_commit_contributor.h',
     'engine/directory_update_handler.cc',
     'engine/directory_update_handler.h',
-    'engine/directory_type_debug_info_emitter.cc',
-    'engine/directory_type_debug_info_emitter.h',
     'engine/get_commit_ids.cc',
     'engine/get_commit_ids.h',
     'engine/get_updates_delegate.cc',
@@ -76,6 +74,10 @@
     'engine/sync_cycle_event.h',
     'engine/sync_engine_event_listener.cc',
     'engine/sync_engine_event_listener.h',
+    'engine/sync_scheduler.cc',
+    'engine/sync_scheduler.h',
+    'engine/sync_scheduler_impl.cc',
+    'engine/sync_scheduler_impl.h',
     'engine/syncer.cc',
     'engine/syncer.h',
     'engine/syncer_proto_util.cc',
@@ -83,10 +85,6 @@
     'engine/syncer_types.h',
     'engine/syncer_util.cc',
     'engine/syncer_util.h',
-    'engine/sync_scheduler.cc',
-    'engine/sync_scheduler.h',
-    'engine/sync_scheduler_impl.cc',
-    'engine/sync_scheduler_impl.h',
     'engine/traffic_logger.cc',
     'engine/traffic_logger.h',
     'engine/update_applicator.cc',
@@ -109,6 +107,8 @@
     'sessions/data_type_tracker.cc',
     'sessions/data_type_tracker.h',
     'sessions/debug_info_getter.h',
+    'sessions/directory_type_debug_info_emitter.cc',
+    'sessions/directory_type_debug_info_emitter.h',
     'sessions/model_type_registry.cc',
     'sessions/model_type_registry.h',
     'sessions/nudge_tracker.cc',
@@ -186,12 +186,12 @@
     'util/extensions_activity.h',
     'util/get_session_name.cc',
     'util/get_session_name.h',
-    'util/get_session_name_ios.mm',
     'util/get_session_name_ios.h',
+    'util/get_session_name_ios.mm',
     'util/get_session_name_linux.cc',
     'util/get_session_name_linux.h',
-    'util/get_session_name_mac.mm',
     'util/get_session_name_mac.h',
+    'util/get_session_name_mac.mm',
     'util/get_session_name_win.cc',
     'util/get_session_name_win.h',
     'util/logging.cc',