Remove variable rewrites and the unneccesary Slot class.

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index b5fdf4902639d1a5db8ca9643d18478ea543caba..01d35a7d2da1d90dd6542b2aab46e36984633d14 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -455,12 +455,11 @@ class HEnvironment: public ZoneObject {
   // by 1 (receiver is parameter index -1 but environment index 0).
   // Stack-allocated local indices are shifted by the number of parameters.
   int IndexFor(Variable* variable) const {
-    Slot* slot = variable->AsSlot();
-    ASSERT(slot != NULL && slot->IsStackAllocated());
-    int shift = (slot->type() == Slot::PARAMETER)
+    ASSERT(variable->IsStackAllocated());
+    int shift = variable->IsParameter()
         ? 1
         : parameter_count_ + specials_count_;
-    return slot->index() + shift;
+    return variable->index() + shift;
   }
 
   Handle<JSFunction> closure_;