Update UnloadReference to use new virtual frame.

src/codegen-ia32.cc

Index: src/codegen-ia32.cc
===================================================================
--- src/codegen-ia32.cc	(revision 1019)
+++ src/codegen-ia32.cc	(working copy)
@@ -544,14 +544,17 @@
 void CodeGenerator::UnloadReference(Reference* ref) {
   // Pop a reference from the stack while preserving TOS.
   Comment cmnt(masm_, "[ UnloadReference");
+  Result top(this);
   int size = ref->size();
   if (size == 1) {
-    frame_->EmitPop(eax);
-    __ mov(frame_->Top(), eax);
+    top = frame_->Pop();
+    // Replace Drop(), Push() sequence with ReplaceTop().
+    frame_->Drop();
+    frame_->Push(&top);
   } else if (size > 1) {
-    frame_->EmitPop(eax);
+    top = frame_->Pop();
     frame_->Drop(size);
-    frame_->EmitPush(eax);
+    frame_->Push(&top);
   }
 }