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 be72b78269e5eeb1d3242a2f1aabd584d5e65872..c58a9add57134e4b347284e0aa5073e80a1a2720 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -1120,6 +1120,11 @@ void ContextExtension::ContextExtensionVerify() {
   VerifyObjectField(kExtensionOffset);
 }
 
+void ConstantElementsPair::ConstantElementsPairVerify() {
+  CHECK(IsConstantElementsPair());
+  VerifySmiField(kElementsKindOffset);
+  VerifyObjectField(kConstantValuesOffset);
+}
 
 void AccessorInfo::AccessorInfoVerify() {
   CHECK(IsAccessorInfo());