Introduce HasPendingMicrotasks API.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 7cf525d3e157a052dd78f21e25df1432518ee9c1..73d85ef0b5820796bc5329ebea1ee14dfcfb488e 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -2313,9 +2313,11 @@ void Isolate::RunMicrotasks() {
     Handle<FixedArray> queue(heap()->microtask_queue(), this);
     DCHECK(num_tasks <= queue->length());
     set_pending_microtask_count(0);
+    set_running_microtask_count(num_tasks);
     heap()->set_microtask_queue(heap()->empty_fixed_array());
 
     for (int i = 0; i < num_tasks; i++) {
+      set_running_microtask_count(num_tasks - i - 1);
       HandleScope scope(this);
       Handle<Object> microtask(queue->get(i), this);
       if (microtask->IsJSFunction()) {
@@ -2333,6 +2335,7 @@ void Isolate::RunMicrotasks() {
           // Clear out any remaining callbacks in the queue.
           heap()->set_microtask_queue(heap()->empty_fixed_array());
           set_pending_microtask_count(0);
+          set_running_microtask_count(0);
           return;
         }
       } else {
@@ -2348,6 +2351,11 @@ void Isolate::RunMicrotasks() {
 }
 
 
+bool Isolate::HasMoreMicrotasksToRun() const {
+  return pending_microtask_count() || running_microtask_count();
+}
+
+
 void Isolate::SetUseCounterCallback(v8::Isolate::UseCounterCallback callback) {
   DCHECK(!use_counter_callback_);
   use_counter_callback_ = callback;