Introduce {ConstantElementsPair} struct for type safety.

src/compiler/js-operator.cc

Index: src/compiler/js-operator.cc
diff --git a/src/compiler/js-operator.cc b/src/compiler/js-operator.cc
index f577a455a8ee06c3a78fac6bd97eb9c4722be1f1..4aa37da9650f1de7ea7c0fc1bc9fa60bff9d81a8 100644
--- a/src/compiler/js-operator.cc
+++ b/src/compiler/js-operator.cc
@@ -854,8 +854,8 @@ const Operator* JSOperatorBuilder::CreateClosure(
 }
 
 const Operator* JSOperatorBuilder::CreateLiteralArray(
-    Handle<FixedArray> constant_elements, int literal_flags, int literal_index,
-    int number_of_elements) {
+    Handle<ConstantElementsPair> constant_elements, int literal_flags,
+    int literal_index, int number_of_elements) {
   CreateLiteralParameters parameters(constant_elements, number_of_elements,
                                      literal_flags, literal_index);
   return new (zone()) Operator1<CreateLiteralParameters>(        // --