[turbofan] Simplify handling of JSON tracing files.

src/compiler/graph-visualizer.h

Index: src/compiler/graph-visualizer.h
diff --git a/src/compiler/graph-visualizer.h b/src/compiler/graph-visualizer.h
index 1a971a55ed5d4a9c99076bda31add39107a4972c..85b0cf7e0981aa97ae40ca78ef976cb15274f0b1 100644
--- a/src/compiler/graph-visualizer.h
+++ b/src/compiler/graph-visualizer.h
@@ -8,6 +8,8 @@
 #include <stdio.h>
 #include <iosfwd>
 
+#include "src/base/smart-pointers.h"
+
 namespace v8 {
 namespace internal {
 
@@ -21,8 +23,8 @@ class RegisterAllocationData;
 class Schedule;
 class SourcePositionTable;
 
-FILE* OpenVisualizerLogFile(CompilationInfo* info, const char* phase,
-                            const char* suffix, const char* mode);
+base::SmartArrayPointer<const char> GetVisualizerLogFileName(
+    CompilationInfo* info, const char* phase, const char* suffix);
 
 struct AsJSON {
   AsJSON(const Graph& g, SourcePositionTable* p) : graph(g), positions(p) {}