Introduce LiteralsArray to hide it's implementation.

src/full-codegen/arm/full-codegen-arm.cc

Index: src/full-codegen/arm/full-codegen-arm.cc
diff --git a/src/full-codegen/arm/full-codegen-arm.cc b/src/full-codegen/arm/full-codegen-arm.cc
index d152f9e601bf4abc653faa308564025be174e3e8..d3d53334d4295b493cc6ad40c520532ab6d8067a 100644
--- a/src/full-codegen/arm/full-codegen-arm.cc
+++ b/src/full-codegen/arm/full-codegen-arm.cc
@@ -1498,8 +1498,7 @@ void FullCodeGenerator::VisitRegExpLiteral(RegExpLiteral* expr) {
   // r0 = RegExp literal clone
   __ ldr(r0, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
   __ ldr(r4, FieldMemOperand(r0, JSFunction::kLiteralsOffset));
-  int literal_offset =
-      FixedArray::kHeaderSize + expr->literal_index() * kPointerSize;
+  int literal_offset = LiteralsArray::OffsetOfLiteralAt(expr->literal_index());
   __ ldr(r5, FieldMemOperand(r4, literal_offset));
   __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
   __ cmp(r5, ip);