ART: Print C1vis header only if visualizer enabled

Setting kStringFilter currently suppresses graph dumps of non-matching
methods but their headers are still printed. This fixes the issue.

Change-Id: Ib33fb20fcca2bf409534a824e7f76f1feb85724d
diff --git a/compiler/optimizing/graph_visualizer.h b/compiler/optimizing/graph_visualizer.h
index bc553ae..513bceb 100644
--- a/compiler/optimizing/graph_visualizer.h
+++ b/compiler/optimizing/graph_visualizer.h
@@ -35,9 +35,9 @@
  public:
   HGraphVisualizer(std::ostream* output,
                    HGraph* graph,
-                   const CodeGenerator& codegen,
-                   const char* method_name);
+                   const CodeGenerator& codegen);
 
+  void PrintHeader(const char* method_name) const;
   void DumpGraph(const char* pass_name, bool is_after_pass = true) const;
 
  private: