src: use std::string for trace enabled_categories

A std::string manages its own memory, so using one removes the implicit
assumption that the argv vector passed to node will never be
deallocated. Also, the enabled_categories are used to construct a
std::stringstream, so its simpler to use the standard library
consistently.

PR-URL: #12242
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

src/node.cc

@@ -153,7 +153,7 @@ static node_module* modlist_builtin;
 static node_module* modlist_linked;
 static node_module* modlist_addon;
 static bool trace_enabled = false;
-static const char* trace_enabled_categories = nullptr;
+static std::string trace_enabled_categories;  // NOLINT(runtime/string)
 
 #if defined(NODE_HAVE_I18N_SUPPORT)
 // Path to ICU data (for i18n / Intl)

src/tracing/agent.cc

@@ -10,10 +10,11 @@ namespace node {
 namespace tracing {
 
 using v8::platform::tracing::TraceConfig;
+using std::string;
 
 Agent::Agent() {}
 
-void Agent::Start(v8::Platform* platform, const char* enabled_categories) {
+void Agent::Start(v8::Platform* platform, const string& enabled_categories) {
   platform_ = platform;
 
   int err = uv_loop_init(&tracing_loop_);
@@ -26,7 +27,7 @@ void Agent::Start(v8::Platform* platform, const char* enabled_categories) {
   tracing_controller_ = new TracingController();
 
   TraceConfig* trace_config = new TraceConfig();
-  if (enabled_categories) {
+  if (!enabled_categories.empty()) {
     std::stringstream category_list(enabled_categories);
     while (category_list.good()) {
       std::string category;

src/tracing/agent.h

@@ -12,7 +12,7 @@ namespace tracing {
 class Agent {
  public:
   explicit Agent();
-  void Start(v8::Platform* platform, const char* enabled_categories);
+  void Start(v8::Platform* platform, const std::string& enabled_categories);
   void Stop();
 
  private: