Remove variable rewrites and the unneccesary Slot class.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 7136105806c548426fc7e98c6bacc1e2c29f4ee3..7c19785d9f63a0a3f9b77f222ce4aad997789ca8 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -194,14 +194,14 @@ bool LCodeGen::GeneratePrologue() {
     // Copy parameters into context if necessary.
     int num_parameters = scope()->num_parameters();
     for (int i = 0; i < num_parameters; i++) {
-      Slot* slot = scope()->parameter(i)->AsSlot();
-      if (slot != NULL && slot->type() == Slot::CONTEXT) {
+      Variable* var = scope()->parameter(i);
+      if (var->IsContextSlot()) {
         int parameter_offset = StandardFrameConstants::kCallerSPOffset +
             (num_parameters - 1 - i) * kPointerSize;
         // Load parameter from stack.
         __ mov(eax, Operand(ebp, parameter_offset));
         // Store it in the context.
-        int context_offset = Context::SlotOffset(slot->index());
+        int context_offset = Context::SlotOffset(var->index());
         __ mov(Operand(esi, context_offset), eax);
         // Update the write barrier. This clobbers all involved
         // registers, so we have to use a third register to avoid