IDL compiler: [CustomLegacyCall] interfaces, cleanup header conditional spacing

Source/bindings/templates/callback_interface.h

 {# http://www.chromium.org/blink/coding-style#TOC-License #}
 /*
  * Copyright (C) 2013 Google Inc. 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.
@@ skipping 17 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 {# FIXME: Rename to Python when switch #}
 // This file has been auto-generated by code_generator_v8.pm. DO NOT MODIFY!
 
 #ifndef {{v8_class_name}}_h
 #define {{v8_class_name}}_h
 
-{% if conditional_string %}
-#if {{conditional_string}}
-{% endif %}
+{% filter conditional(conditional_string) %}
 {% for filename in header_includes %}
 #include "{{filename}}"
 {% endfor %}
 
 namespace WebCore {
 
 class ExecutionContext;
 
 class {{v8_class_name}} : public {{cpp_class_name}}, public ActiveDOMCallback {
 public:
@@ skipping 13 matching lines @@
     virtual ExecutionContext* executionContext() const { return ContextLifecycleObserver::executionContext(); }
 
 private:
     {{v8_class_name}}(v8::Handle<v8::Object>, ExecutionContext*);
 
     ScopedPersistent<v8::Object> m_callback;
     RefPtr<DOMWrapperWorld> m_world;
 };
 
 }
-
-{% if conditional_string %}
-#endif // {{conditional_string}}
-{% endif %}
+{% endfilter %}
 #endif // {{v8_class_name}}_h