Introduce LiteralsArray to hide it's implementation.

src/full-codegen/arm64/full-codegen-arm64.cc

Index: src/full-codegen/arm64/full-codegen-arm64.cc
diff --git a/src/full-codegen/arm64/full-codegen-arm64.cc b/src/full-codegen/arm64/full-codegen-arm64.cc
index 43e2b9f55b5a27c5d2df93b559a46bb3e0e1cc93..b53e8ee6cde133fdefe74dde81723ddaea3cd45c 100644
--- a/src/full-codegen/arm64/full-codegen-arm64.cc
+++ b/src/full-codegen/arm64/full-codegen-arm64.cc
@@ -1487,8 +1487,7 @@ void FullCodeGenerator::VisitRegExpLiteral(RegExpLiteral* expr) {
   // x0 = RegExp literal clone
   __ Ldr(x10, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
   __ Ldr(x4, FieldMemOperand(x10, JSFunction::kLiteralsOffset));
-  int literal_offset =
-      FixedArray::kHeaderSize + expr->literal_index() * kPointerSize;
+  int literal_offset = LiteralsArray::OffsetOfLiteralAt(expr->literal_index());
   __ Ldr(x5, FieldMemOperand(x4, literal_offset));
   __ JumpIfNotRoot(x5, Heap::kUndefinedValueRootIndex, &materialized);