sync: Refactor per-datatype throttling

sync/engine/syncer.cc

Index: sync/engine/syncer.cc
diff --git a/sync/engine/syncer.cc b/sync/engine/syncer.cc
index ac6b5eb787e354f94b2d5daab3f6ae9c1b631088..344851c48a0b30a9cd81d1fc5974d684e42607f3 100644
--- a/sync/engine/syncer.cc
+++ b/sync/engine/syncer.cc
@@ -16,6 +16,7 @@
 #include "sync/engine/clear_data_command.h"
 #include "sync/engine/commit.h"
 #include "sync/engine/conflict_resolver.h"
+#include "sync/engine/throttled_data_type_tracker.h"
 #include "sync/engine/download_updates_command.h"
 #include "sync/engine/net/server_connection_manager.h"
 #include "sync/engine/process_commit_response_command.h"
@@ -107,7 +108,8 @@ void Syncer::SyncShare(sessions::SyncSession* session,
 
     switch (current_step) {
       case SYNCER_BEGIN:
-        session->context()->PruneUnthrottledTypes(base::TimeTicks::Now());
+        session->context()->throttled_data_type_tracker()->
+            PruneUnthrottledTypes(base::TimeTicks::Now());
         session->SendEventNotification(SyncEngineEvent::SYNC_CYCLE_BEGIN);
 
         next_step = CLEANUP_DISABLED_TYPES;