refactor: use std::optional in MicrotasksScope (#43621)

avoid an unnecessary heap allocation/free

shell/common/gin_helper/microtasks_scope.cc

@@ -16,8 +16,7 @@ MicrotasksScope::MicrotasksScope(v8::Isolate* isolate,
     if (!ignore_browser_checkpoint)
       v8::MicrotasksScope::PerformCheckpoint(isolate);
   } else {
-    v8_microtasks_scope_ = std::make_unique<v8::MicrotasksScope>(
-        isolate, microtask_queue, scope_type);
+    v8_microtasks_scope_.emplace(isolate, microtask_queue, scope_type);
   }
 }
 

shell/common/gin_helper/microtasks_scope.h

@@ -5,7 +5,7 @@
 #ifndef ELECTRON_SHELL_COMMON_GIN_HELPER_MICROTASKS_SCOPE_H_
 #define ELECTRON_SHELL_COMMON_GIN_HELPER_MICROTASKS_SCOPE_H_
 
-#include <memory>
+#include <optional>
 
 #include "v8/include/v8-forward.h"
 #include "v8/include/v8-microtask-queue.h"
@@ -27,7 +27,7 @@ class MicrotasksScope {
   MicrotasksScope& operator=(const MicrotasksScope&) = delete;
 
  private:
-  std::unique_ptr<v8::MicrotasksScope> v8_microtasks_scope_;
+  std::optional<v8::MicrotasksScope> v8_microtasks_scope_;
 };
 
 }  // namespace gin_helper