[turbofan] Simplify handling of JSON tracing files.

src/compiler/graph-visualizer.cc

Index: src/compiler/graph-visualizer.cc
diff --git a/src/compiler/graph-visualizer.cc b/src/compiler/graph-visualizer.cc
index f431ab5d4d1a68b016045c61d1182363939c74f1..1dc38df0d965c89d50a5ffa3e8db5453295e9845 100644
--- a/src/compiler/graph-visualizer.cc
+++ b/src/compiler/graph-visualizer.cc
@@ -25,9 +25,8 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
-
-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) {
   EmbeddedVector<char, 256> filename(0);
   base::SmartArrayPointer<char> debug_name = info->GetDebugName();
   if (strlen(debug_name.get()) > 0) {
@@ -46,7 +45,11 @@ FILE* OpenVisualizerLogFile(CompilationInfo* info, const char* phase,
   } else {
     SNPrintF(full_filename, "%s-%s.%s", filename.start(), phase, suffix);
   }
-  return base::OS::FOpen(full_filename.start(), mode);
+
+  char* buffer = new char[full_filename.length() + 1];
+  memcpy(buffer, full_filename.start(), full_filename.length());
+  buffer[full_filename.length()] = '\0';
+  return base::SmartArrayPointer<const char>(buffer);
 }