PPC: Introduce LiteralsArray to hide it's implementation.

src/full-codegen/ppc/full-codegen-ppc.cc

Index: src/full-codegen/ppc/full-codegen-ppc.cc
diff --git a/src/full-codegen/ppc/full-codegen-ppc.cc b/src/full-codegen/ppc/full-codegen-ppc.cc
index 8aa7aaca6a557b80d12062f4a9ac34aec9d05143..c86a8df7e676160ecbb7a542638411ba8ee852ea 100644
--- a/src/full-codegen/ppc/full-codegen-ppc.cc
+++ b/src/full-codegen/ppc/full-codegen-ppc.cc
@@ -1469,8 +1469,7 @@ void FullCodeGenerator::VisitRegExpLiteral(RegExpLiteral* expr) {
   // r3 = RegExp literal clone
   __ LoadP(r3, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
   __ LoadP(r7, FieldMemOperand(r3, JSFunction::kLiteralsOffset));
-  int literal_offset =
-      FixedArray::kHeaderSize + expr->literal_index() * kPointerSize;
+  int literal_offset = LiteralsArray::OffsetOfLiteralAt(expr->literal_index());
   __ LoadP(r8, FieldMemOperand(r7, literal_offset), r0);
   __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
   __ cmp(r8, ip);