Fixed preparser for try statement. Tiny cleanup.

src/preparser.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 452 matching lines @@
     bool IsInsideWith() { return with_nesting_count_ != 0; }
     bool is_classic_mode() {
       return language_mode_ == i::CLASSIC_MODE;
     }
     i::LanguageMode language_mode() {
       return language_mode_;
     }
     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_;
     Scope* const prev_;
     const ScopeType type_;
     int materialized_literal_count_;
     int expected_properties_;
     int with_nesting_count_;
     i::LanguageMode language_mode_;
   };
@@ skipping 167 matching lines @@
   bool stack_overflow_;
   bool allow_lazy_;
   bool allow_modules_;
   bool allow_natives_syntax_;
   bool parenthesized_function_;
   bool harmony_scoping_;
 };
 } }  // v8::preparser
 
 #endif  // V8_PREPARSER_H