Only swap undefined for the global object if necessary in the prologue

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 788fda4a33923bf9ed68cc5ae66a7b5c39eae170..9bdc070300512b44f0c6ea5ba292b8530655ef9f 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -3496,7 +3496,6 @@ HGraph::HGraph(CompilationInfo* info)
       info_(info),
       zone_(info->zone()),
       is_recursive_(false),
-      this_has_uses_(false),
       use_optimistic_licm_(false),
       depends_on_empty_array_proto_elements_(false),
       type_change_checksum_(0),
@@ -5402,10 +5401,6 @@ HValue* HOptimizedGraphBuilder::BuildContextChainWalk(Variable* var) {
 
 
 void HOptimizedGraphBuilder::VisitVariableProxy(VariableProxy* expr) {
-  if (expr->is_this()) {
-    graph()->MarkThisHasUses();
-  }
-
   DCHECK(!HasStackOverflow());
   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());