dawn_node: Prevent setImmediate() being queued multiple times

The AsyncRunner will enqueue a call to `Device::Tick()` when the runner count moves from 0 async tasks to 1.

It has been observed that some 'async' tasks are actually synchronious, which results in multiple tick callbacks being enqueued before the first has a chance to run.
Fix this by using another boolean to track whether the function has been queued.

Bug: dawn:1127
Change-Id: I7dd81d33d601bf1d3cefb5c4dad6c237883e51ee
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/66820
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/dawn_node/binding/AsyncRunner.cpp

@@ -37,6 +37,10 @@ namespace wgpu { namespace binding {
     void AsyncRunner::QueueTick() {
         // TODO(crbug.com/dawn/1127): We probably want to reduce the frequency at which this gets
         // called.
+        if (tick_queued_) {
+            return;
+        }
+        tick_queued_ = true;
         env_.Global()
             .Get("setImmediate")
             .As<Napi::Function>()
@@ -44,6 +48,7 @@ namespace wgpu { namespace binding {
                 // TODO(crbug.com/dawn/1127): Create once, reuse.
                 Napi::Function::New(env_,
                                     [this](const Napi::CallbackInfo&) {
+                                        tick_queued_ = false;
                                         if (count_ > 0) {
                                             device_.Tick();
                                             QueueTick();

src/dawn_node/binding/AsyncRunner.h

@@ -45,6 +45,7 @@ namespace wgpu { namespace binding {
         Napi::Env env_;
         wgpu::Device const device_;
         uint64_t count_ = 0;
+        bool tick_queued_ = false;
     };
 
     // AsyncTask is a RAII helper for calling AsyncRunner::Begin() on construction, and