[Sync] Replace typedef with using.

components/sync/base/ordinal_unittest.cc

Index: components/sync/base/ordinal_unittest.cc
diff --git a/components/sync/base/ordinal_unittest.cc b/components/sync/base/ordinal_unittest.cc
index 246c874145e4f798c81c7f6eb5d1eca153e59064..3f61e50612d5b3c3bf77588125a84f75a4e86f24 100644
--- a/components/sync/base/ordinal_unittest.cc
+++ b/components/sync/base/ordinal_unittest.cc
@@ -31,9 +31,9 @@ struct LargeOrdinalTraits {
   static const size_t kMinLength = 1;
 };
 
-typedef Ordinal<TestOrdinalTraits> TestOrdinal;
-typedef Ordinal<LongOrdinalTraits> LongOrdinal;
-typedef Ordinal<LargeOrdinalTraits> LargeOrdinal;
+using TestOrdinal = Ordinal<TestOrdinalTraits>;
+using LongOrdinal = Ordinal<LongOrdinalTraits>;
+using LargeOrdinal = Ordinal<LargeOrdinalTraits>;
 
 static_assert(TestOrdinal::kZeroDigit == '0',
               "incorrect TestOrdinal zero digit");