Simple support for const variables in Crankshaft....

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h	(revision 8094)
+++ src/hydrogen-instructions.h	(working copy)
@@ -168,6 +168,7 @@
   V(TypeofIs)                                  \
   V(UnaryMathOperation)                        \
   V(UnknownOSRValue)                           \
+  V(UseConst)                                  \
   V(ValueOf)
 
 #define GVN_FLAG_LIST(V)                       \
@@ -1019,6 +1020,18 @@
 };
 
 
+class HUseConst: public HUnaryOperation {
+ public:
+  explicit HUseConst(HValue* old_value) : HUnaryOperation(old_value) { }
+
+  virtual Representation RequiredInputRepresentation(int index) const {
+    return Representation::None();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(UseConst)
+};
+
+
 class HForceRepresentation: public HTemplateInstruction<1> {
  public:
   HForceRepresentation(HValue* value, Representation required_representation) {