Guard the Flutter Skia event tracer category flags with a lock (flutter/engine#31416)

engine/src/flutter/shell/common/skia_event_tracer_impl.cc

@@ -274,6 +274,7 @@ class FlutterEventTracer : public SkEventTracer {
 
   const uint8_t* getCategoryGroupEnabled(const char* name) override {
     // Skia will only use long-lived string literals as event names.
+    std::lock_guard<std::mutex> lock(flag_map_mutex_);
     auto flag_it = category_flag_map_.find(name);
     if (flag_it == category_flag_map_.end()) {
       bool allowed;
@@ -295,6 +296,7 @@ class FlutterEventTracer : public SkEventTracer {
 
   const char* getCategoryGroupName(
       const uint8_t* category_enabled_flag) override {
+    std::lock_guard<std::mutex> lock(flag_map_mutex_);
     auto reverse_it = reverse_flag_map_.find(category_enabled_flag);
     if (reverse_it != reverse_flag_map_.end()) {
       return reverse_it->second;
@@ -306,6 +308,7 @@ class FlutterEventTracer : public SkEventTracer {
  private:
   uint8_t enabled_;
   std::optional<std::set<std::string>> allowlist_;
+  std::mutex flag_map_mutex_;
   std::map<const char*, uint8_t> category_flag_map_;
   std::map<const uint8_t*, const char*> reverse_flag_map_;
   const uint8_t* shaders_category_flag_;

engine/src/flutter/shell/common/skia_event_tracer_impl.h

@@ -5,6 +5,7 @@
 #ifndef FLUTTER_SHELL_COMMON_SKIA_EVENT_TRACER_IMPL_H_
 #define FLUTTER_SHELL_COMMON_SKIA_EVENT_TRACER_IMPL_H_
 
+#include <mutex>
 #include <optional>
 #include <string>
 #include <vector>