Expose the depth of MicrotasksScope per MicrotaskQueue

Blink used to use v8::MicrotasksScope::GetCurrentDepth() to get the
number of nested MicrotasksScope for the default microtask queue.
However, there was no corresponding one for non-default queues.

Change-Id: I1c2472ba19b1a11cb968f02119d91d92867c6e02
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1567705Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60862}

include/v8.h

@@ -6817,6 +6817,12 @@ class V8_EXPORT MicrotaskQueue {
    */
   virtual bool IsRunningMicrotasks() const = 0;
 
+  /**
+   * Returns the current depth of nested MicrotasksScope that has
+   * kRunMicrotasks.
+   */
+  virtual int GetMicrotasksScopeDepth() const = 0;
+
  private:
   friend class internal::MicrotaskQueue;
   MicrotaskQueue() = default;

src/microtask-queue.cc

@@ -211,6 +211,10 @@ void MicrotaskQueue::IterateMicrotasks(RootVisitor* visitor) {
   }
 }
 
+int MicrotaskQueue::GetMicrotasksScopeDepth() const {
+  return microtasks_depth_;
+}
+
 void MicrotaskQueue::AddMicrotasksCompletedCallback(
     MicrotasksCompletedCallbackWithData callback, void* data) {
   CallbackWithData callback_with_data(callback, data);

src/microtask-queue.h

@@ -62,7 +62,7 @@ class V8_EXPORT_PRIVATE MicrotaskQueue final : public v8::MicrotaskQueue {
   // invocation, which happens when depth reaches zero.
   void IncrementMicrotasksScopeDepth() { ++microtasks_depth_; }
   void DecrementMicrotasksScopeDepth() { --microtasks_depth_; }
-  int GetMicrotasksScopeDepth() const { return microtasks_depth_; }
+  int GetMicrotasksScopeDepth() const override;
 
   // Possibly nested microtasks suppression scopes prevent microtasks
   // from running.