MIPS: Fix r19360 "Improve positions tracking inside the HGraphBuilder."

BUG=
R=vegorov@chromium.org

Review URL: https://codereview.chromium.org/164033002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19364 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-mips.cc

@@ -848,7 +848,6 @@ void LChunkBuilder::DoBasicBlock(HBasicBlock* block, HBasicBlock* next_block) {
 void LChunkBuilder::VisitInstruction(HInstruction* current) {
   HInstruction* old_current = current_instruction_;
   current_instruction_ = current;
-  if (current->has_position()) position_ = current->position();
 
   LInstruction* instr = NULL;
   if (current->CanReplaceWithDummyUses()) {

src/mips/lithium-mips.h

@@ -2554,7 +2554,6 @@ class LChunkBuilder V8_FINAL : public LChunkBuilderBase {
         current_block_(NULL),
         next_block_(NULL),
         allocator_(allocator),
-        position_(RelocInfo::kNoPosition),
         instruction_pending_deoptimization_environment_(NULL),
         pending_deoptimization_ast_id_(BailoutId::None()) { }
 
@@ -2690,7 +2689,6 @@ class LChunkBuilder V8_FINAL : public LChunkBuilderBase {
   HBasicBlock* current_block_;
   HBasicBlock* next_block_;
   LAllocator* allocator_;
-  int position_;
   LInstruction* instruction_pending_deoptimization_environment_;
   BailoutId pending_deoptimization_ast_id_;