Use NeedsContext() instead of comparing num_heap_slots().

src/crankshaft/x64/lithium-x64.cc

Index: src/crankshaft/x64/lithium-x64.cc
diff --git a/src/crankshaft/x64/lithium-x64.cc b/src/crankshaft/x64/lithium-x64.cc
index 42451690af1469631318839506f55890e9272aa2..b16ea7b8913aa9b9b7d1233f4ee54fa99823fb74 100644
--- a/src/crankshaft/x64/lithium-x64.cc
+++ b/src/crankshaft/x64/lithium-x64.cc
@@ -907,7 +907,7 @@ LInstruction* LChunkBuilder::DoGoto(HGoto* 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;