Fixed preparser for try statement. Tiny cleanup.

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index f3a43475dfe96bb3d3fd78abfecbf42862883b3c..13261f7a5b945f6b278a5ac9d450557bdce3e168 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -470,8 +470,19 @@ class PreParser {
     void set_language_mode(i::LanguageMode language_mode) {
       language_mode_ = language_mode;
     }
-    void EnterWith() { with_nesting_count_++; }
-    void LeaveWith() { with_nesting_count_--; }
+
+    class InsideWith {
+     public:
+      explicit InsideWith(Scope* scope) : scope_(scope) {
+        scope->with_nesting_count_++;
+      }
+
+      ~InsideWith() { scope_->with_nesting_count_--; }
+
+     private:
+      Scope* scope_;
+      DISALLOW_COPY_AND_ASSIGN(InsideWith);
+    };
 
    private:
     Scope** const variable_;