Support fast case for-in in Crankshaft.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index aff496f62960749163fba59b82a3b549ff83a6a7..8582d018c347c3e4951c8b0a80f0c240c850c473 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1295,6 +1295,11 @@ class MacroAssembler: public Assembler {
   void EnterFrame(StackFrame::Type type);
   void LeaveFrame(StackFrame::Type type);
 
+  // Expects object in rax and returns map with validated enum cache
+  // in rax.  Assumes that any other register can be used as a scratch.
+  void CheckEnumCache(Register null_value,
+                      Label* call_runtime);
+
  private:
   // Order general registers are pushed by Pushad.
   // rax, rcx, rdx, rbx, rsi, rdi, r8, r9, r11, r14, r15.