Fix arrow functions requiring context without slots.

src/arm/full-codegen-arm.cc

Index: src/arm/full-codegen-arm.cc
diff --git a/src/arm/full-codegen-arm.cc b/src/arm/full-codegen-arm.cc
index a792d9f3d2ed33728f80f293a7b0bf4fa9052965..d7586817a31461c8081bb996705ae579de5ccd02 100644
--- a/src/arm/full-codegen-arm.cc
+++ b/src/arm/full-codegen-arm.cc
@@ -191,17 +191,17 @@ void FullCodeGenerator::Generate() {
   bool function_in_register = true;
 
   // Possibly allocate a local context.
-  int heap_slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
-  if (heap_slots > 0) {
+  if (info->scope()->num_heap_slots() > 0) {
     // Argument to NewContext is the function, which is still in r1.
     Comment cmnt(masm_, "[ Allocate context");
     bool need_write_barrier = true;
+    int slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
     if (info->scope()->is_script_scope()) {
       __ push(r1);
       __ Push(info->scope()->GetScopeInfo(info->isolate()));
       __ CallRuntime(Runtime::kNewScriptContext, 2);
-    } else if (heap_slots <= FastNewContextStub::kMaximumSlots) {
-      FastNewContextStub stub(isolate(), heap_slots);
+    } else if (slots <= FastNewContextStub::kMaximumSlots) {
+      FastNewContextStub stub(isolate(), slots);
       __ CallStub(&stub);
       // Result of FastNewContextStub is always in new space.
       need_write_barrier = false;