Refactoring using TempAssign.

src/utils.h

Index: src/utils.h
===================================================================
--- src/utils.h	(revision 977)
+++ src/utils.h	(working copy)
@@ -377,12 +377,14 @@
 template <typename T>
 class TempAssign {
  public:
-  TempAssign(T* var, T value): var_(var), old_value_(*var) {
+  TempAssign(T* var, const T& value): var_(var), old_value_(*var) {
     *var = value;
   }
 
   ~TempAssign() { *var_ = old_value_; }
 
+  const T& old_value() const { return old_value_; };
+
  private:
   T* var_;
   T old_value_;