Introduce {ConstantElementsPair} struct for type safety.

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index 07a695e9f69d42b67bfd883d5f6639bbb1789919..51969c5697204230eb06decd9afe8a9b559bcccc 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -1108,6 +1108,11 @@ void ContextExtension::ContextExtensionVerify() {
   VerifyObjectField(kExtensionOffset);
 }
 
+void ConstantElementsPair::ConstantElementsPairVerify() {
+  CHECK(IsConstantElementsPair());
+  VerifySmiField(kElementsKindOffset);
+  VerifyObjectField(kConstantValuesOffset);
+}
 
 void AccessorInfo::AccessorInfoVerify() {
   CHECK(IsAccessorInfo());