[turbofan]: Small visualizer cleanup and fix for string handling

src/compiler/graph-visualizer.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_GRAPH_VISUALIZER_H_
 #define V8_COMPILER_GRAPH_VISUALIZER_H_
 
 #include <iosfwd>
 
 namespace v8 {
 namespace internal {
 
 class CompilationInfo;
 
 namespace compiler {
 
 class Graph;
 class InstructionSequence;
 class RegisterAllocator;
 class Schedule;
 class SourcePositionTable;
 
+FILE* OpenVisualizerLogFile(CompilationInfo* info, const char* phase,
+                            const char* suffix, const char* mode);
 
 struct AsDOT {
   explicit AsDOT(const Graph& g) : graph(g) {}
   const Graph& graph;
 };
 
 std::ostream& operator<<(std::ostream& os, const AsDOT& ad);
 
 
 struct AsJSON {
@@ skipping 43 matching lines @@
 std::ostream& operator<<(std::ostream& os, const AsDOT& ad);
 std::ostream& operator<<(std::ostream& os, const AsC1VCompilation& ac);
 std::ostream& operator<<(std::ostream& os, const AsC1V& ac);
 std::ostream& operator<<(std::ostream& os, const AsC1VAllocator& ac);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_GRAPH_VISUALIZER_H_