Use NeedsContext() instead of comparing num_heap_slots().

src/crankshaft/x87/lithium-x87.cc

Index: src/crankshaft/x87/lithium-x87.cc
diff --git a/src/crankshaft/x87/lithium-x87.cc b/src/crankshaft/x87/lithium-x87.cc
index f614b93c9c631eb49b923b751e7dd68946018e87..b0cc7330c5c27c16f415dd8cbe3f14f2330040c2 100644
--- a/src/crankshaft/x87/lithium-x87.cc
+++ b/src/crankshaft/x87/lithium-x87.cc
@@ -925,7 +925,7 @@ void LChunkBuilder::AddInstruction(LInstruction* instr,
 
 LInstruction* LChunkBuilder::DoPrologue(HPrologue* instr) {
   LInstruction* result = new (zone()) LPrologue();
-  if (info_->scope()->num_heap_slots() > 0) {
+  if (info_->scope()->NeedsContext()) {
     result = MarkAsCall(result, instr);
   }
   return result;