Introduce MicrotasksCompletedCallback.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 6d1c8d87eefe7294a03bb37dd38b7de7f88ff865..d9c2cca14db21e52b88a540c38a7ffa16ec08529 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -5047,7 +5047,8 @@ class PromiseRejectMessage {
 
 typedef void (*PromiseRejectCallback)(PromiseRejectMessage message);
 
-// --- Microtask Callback ---
+// --- Microtasks Callbacks ---
+typedef void (*MicrotasksCompletedCallback)(Isolate*);
 typedef void (*MicrotaskCallback)(void* data);
 
 // --- Failed Access Check Callback ---
@@ -5888,6 +5889,25 @@ class V8_EXPORT Isolate {
   bool WillAutorunMicrotasks() const;
 
   /**
+   * Experimental: adds a callback to notify the host application after
+   * microtasks were run. The callback is triggered by explicit RunMicrotasks
+   * call or automatic microtasks execution (see SetAutorunMicrotasks).
+   *
+   * Callback will trigger even if microtasks were attempted to run,
+   * but the microtasks queue was empty and no single microtask was actually
+   * executed.
+   *
+   * Executing scriptsinside the callback will not re-trigger microtasks and
+   * the callback.
+   */
+  void AddMicrotasksCompletedCallback(MicrotasksCompletedCallback callback);
+
+  /**
+   * Removes callback that was installed by AddMicrotasksCompletedCallback.
+   */
+  void RemoveMicrotasksCompletedCallback(MicrotasksCompletedCallback callback);
+
+  /**
    * Sets a callback for counting the number of times a feature of V8 is used.
    */
   void SetUseCounterCallback(UseCounterCallback callback);