Use NeedsContext() instead of comparing num_heap_slots().

src/crankshaft/mips/lithium-codegen-mips.cc

Index: src/crankshaft/mips/lithium-codegen-mips.cc
diff --git a/src/crankshaft/mips/lithium-codegen-mips.cc b/src/crankshaft/mips/lithium-codegen-mips.cc
index fa345e5173c21e6eb302bebc5725682422de0aac..2453ede9ff3eb1f492bd1c87732cf446edd19214 100644
--- a/src/crankshaft/mips/lithium-codegen-mips.cc
+++ b/src/crankshaft/mips/lithium-codegen-mips.cc
@@ -171,7 +171,7 @@ void LCodeGen::DoPrologue(LPrologue* instr) {
   Comment(";;; Prologue begin");
 
   // Possibly allocate a local context.
-  if (info()->scope()->num_heap_slots() > 0) {
+  if (info()->scope()->NeedsContext()) {
     Comment(";;; Allocate local context");
     bool need_write_barrier = true;
     // Argument to NewContext is the function, which is in a1.