Unify the handling of comparinsons against null and undefined.

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
===================================================================
--- src/x64/lithium-x64.h	(revision 9305)
+++ src/x64/lithium-x64.h	(working copy)
@@ -107,7 +107,7 @@
   V(Integer32ToDouble)                          \
   V(InvokeFunction)                             \
   V(IsConstructCallAndBranch)                   \
-  V(IsNullAndBranch)                            \
+  V(IsNilAndBranch)                             \
   V(IsObjectAndBranch)                          \
   V(IsSmiAndBranch)                             \
   V(IsUndetectableAndBranch)                    \
@@ -609,17 +609,18 @@
 };
 
 
-class LIsNullAndBranch: public LControlInstruction<1, 1> {
+class LIsNilAndBranch: public LControlInstruction<1, 1> {
  public:
-  LIsNullAndBranch(LOperand* value, LOperand* temp) {
+  LIsNilAndBranch(LOperand* value, LOperand* temp) {
     inputs_[0] = value;
     temps_[0] = temp;
   }
 
-  DECLARE_CONCRETE_INSTRUCTION(IsNullAndBranch, "is-null-and-branch")
-  DECLARE_HYDROGEN_ACCESSOR(IsNullAndBranch)
+  DECLARE_CONCRETE_INSTRUCTION(IsNilAndBranch, "is-nil-and-branch")
+  DECLARE_HYDROGEN_ACCESSOR(IsNilAndBranch)
 
-  bool is_strict() const { return hydrogen()->is_strict(); }
+  EqualityKind kind() const { return hydrogen()->kind(); }
+  NilValue nil() const { return hydrogen()->nil(); }
 
   virtual void PrintDataTo(StringStream* stream);
 };