[crankshaft] Fixing ES6 tail call elimination.

src/crankshaft/x64/lithium-x64.h

Index: src/crankshaft/x64/lithium-x64.h
diff --git a/src/crankshaft/x64/lithium-x64.h b/src/crankshaft/x64/lithium-x64.h
index 78bd6ed5e7a815c26b862bd63bc3e144709af4e9..4831e62b51c75c9b38639879013ca391be6ca74f 100644
--- a/src/crankshaft/x64/lithium-x64.h
+++ b/src/crankshaft/x64/lithium-x64.h
@@ -221,6 +221,13 @@ class LInstruction : public ZoneObject {
   void MarkAsCall() { bit_field_ = IsCallBits::update(bit_field_, true); }
   bool IsCall() const { return IsCallBits::decode(bit_field_); }
 
+  void MarkAsSyntacticTailCall() {
+    bit_field_ = IsSyntacticTailCallBits::update(bit_field_, true);
+  }
+  bool IsSyntacticTailCall() const {
+    return IsSyntacticTailCallBits::decode(bit_field_);
+  }
+
   // Interface to the register allocator and iterators.
   bool ClobbersTemps() const { return IsCall(); }
   bool ClobbersRegisters() const { return IsCall(); }
@@ -259,6 +266,8 @@ class LInstruction : public ZoneObject {
   virtual LOperand* TempAt(int i) = 0;
 
   class IsCallBits: public BitField<bool, 0, 1> {};
+  class IsSyntacticTailCallBits : public BitField<bool, IsCallBits::kNext, 1> {
+  };
 
   LEnvironment* environment_;
   SetOncePointer<LPointerMap> pointer_map_;