PPC: Introduce LiteralsArray to hide it's implementation.

Port d8cdd695

Original commit message:
    The LiteralsArray will soon hold a type feedback vector. Code treats it as an
    ordinary fixed array, and needs to stop that.

R=mvstanton@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1373823003

Cr-Commit-Position: refs/heads/master@{#31035}

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

@@ -1464,8 +1464,7 @@ 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);

src/ppc/lithium-codegen-ppc.cc

@@ -5695,7 +5695,7 @@ void LCodeGen::DoRegExpLiteral(LRegExpLiteral* instr) {
   // r3 = regexp literal clone.
   // r5 and r7-r9 are used as temporaries.
   int literal_offset =
-      FixedArray::OffsetOfElementAt(instr->hydrogen()->literal_index());
+      LiteralsArray::OffsetOfLiteralAt(instr->hydrogen()->literal_index());
   __ Move(r10, instr->hydrogen()->literals());
   __ LoadP(r4, FieldMemOperand(r10, literal_offset));
   __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);