Introduce HasPendingMicrotasks API.

src/isolate.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdlib.h>
 
 #include "src/v8.h"
 
 #include "src/ast.h"
 #include "src/base/platform/platform.h"
@@ skipping 2295 matching lines @@
   // Increase call depth to prevent recursive callbacks.
   v8::Isolate::SuppressMicrotaskExecutionScope suppress(
       reinterpret_cast<v8::Isolate*>(this));
 
   while (pending_microtask_count() > 0) {
     HandleScope scope(this);
     int num_tasks = pending_microtask_count();
     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()) {
         Handle<JSFunction> microtask_function =
             Handle<JSFunction>::cast(microtask);
         SaveContext save(this);
         set_context(microtask_function->context()->native_context());
         MaybeHandle<Object> maybe_exception;
         MaybeHandle<Object> result =
             Execution::TryCall(microtask_function, factory()->undefined_value(),
                                0, NULL, &maybe_exception);
         // If execution is terminating, just bail out.
         Handle<Object> exception;
         if (result.is_null() && maybe_exception.is_null()) {
           // 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 {
         Handle<CallHandlerInfo> callback_info =
             Handle<CallHandlerInfo>::cast(microtask);
         v8::MicrotaskCallback callback =
             v8::ToCData<v8::MicrotaskCallback>(callback_info->callback());
         void* data = v8::ToCData<void*>(callback_info->data());
         callback(data);
       }
     }
   }
 }
 
 
+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;
 }
 
 
 void Isolate::CountUsage(v8::Isolate::UseCounterFeature feature) {
   if (use_counter_callback_) {
     use_counter_callback_(reinterpret_cast<v8::Isolate*>(this), feature);
   }
@@ skipping 25 matching lines @@
   if (prev_ && prev_->Intercept(flag)) return true;
   // Then check whether this scope intercepts.
   if ((flag & intercept_mask_)) {
     intercepted_flags_ |= flag;
     return true;
   }
   return false;
 }
 
 } }  // namespace v8::internal