[Cleanup] Migrate ImporterList to use the TaskScheduler API.

chrome/browser/importer/importer_list.h

Index: chrome/browser/importer/importer_list.h
diff --git a/chrome/browser/importer/importer_list.h b/chrome/browser/importer/importer_list.h
index b7a245232bda3234d5ff276bfe03064663217289..3fa892ebb32f0b6ebab3a19f774c201f24432c0c 100644
--- a/chrome/browser/importer/importer_list.h
+++ b/chrome/browser/importer/importer_list.h
@@ -13,6 +13,7 @@
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/sequence_checker.h"
 #include "base/strings/string16.h"
 #include "chrome/common/importer/importer_data_types.h"
 
@@ -54,6 +55,8 @@ class ImporterList {
   // The list of profiles with the default one first.
   std::vector<importer::SourceProfile> source_profiles_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   base::WeakPtrFactory<ImporterList> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ImporterList);