Introduce {ConstantElementsPair} struct for type safety.

src/full-codegen/s390/full-codegen-s390.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_S390
 
 #include "src/full-codegen/full-codegen.h"
 #include "src/ast/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/code-factory.h"
@@ skipping 1246 matching lines @@
   if (result_saved) {
     context()->PlugTOS();
   } else {
     context()->Plug(r2);
   }
 }
 
 void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
   Comment cmnt(masm_, "[ ArrayLiteral");
 
-  Handle<FixedArray> constant_elements = expr->constant_elements();
+  Handle<ConstantElementsPair> constant_elements = expr->constant_elements();
   bool has_fast_elements =
       IsFastObjectElementsKind(expr->constant_elements_kind());
-  Handle<FixedArrayBase> constant_elements_values(
-      FixedArrayBase::cast(constant_elements->get(1)));
 
   AllocationSiteMode allocation_site_mode = TRACK_ALLOCATION_SITE;
   if (has_fast_elements && !FLAG_allocation_site_pretenuring) {
     // If the only customer of allocation sites is transitioning, then
     // we can turn it off if we don't have anywhere else to transition to.
     allocation_site_mode = DONT_TRACK_ALLOCATION_SITE;
   }
 
   __ LoadP(r5, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
   __ LoadSmiLiteral(r4, Smi::FromInt(expr->literal_index()));
@@ skipping 1513 matching lines @@
   DCHECK(kOSRBranchInstruction == br_instr);
 
   DCHECK(interrupt_address ==
          isolate->builtins()->OnStackReplacement()->entry());
   return ON_STACK_REPLACEMENT;
 }
 
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_TARGET_ARCH_S390