Throw an exception when AudioWorkletNode is created on a destroyed ExecutionContext

The repro case creates an AudioWorkletNode after the ExecutionContext
goes away. (detached iframe) AudioWorkletNode is equipped with a
MessageChannel which requires a valid ExecutionContext.

AudioWorkletNode is not fully functional without message ports anyway,
so we can throw an exception in this case.

Test: Locally confirmed the ASAN build doesn't crash with the repro anymore.
Bug: 1050419
Change-Id: I52af9f877e2ad31923c6380dc0732eb6c97ab407
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2051386Reviewed-by: Raymond Toy <rtoy@chromium.org>
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740754}

third_party/blink/renderer/modules/webaudio/audio_worklet_node.cc

@@ -311,6 +311,13 @@ AudioWorkletNode* AudioWorkletNode::Create(
     return nullptr;
   }
 
+  if (context->IsContextClosed()) {
+    exception_state.ThrowDOMException(
+        DOMExceptionCode::kInvalidStateError,
+        "AudioWorkletNode cannot be created: No execution context available.");
+    return nullptr;
+  }
+
   auto* channel =
       MakeGarbageCollected<MessageChannel>(context->GetExecutionContext());
   MessagePortChannel processor_port_channel = channel->port2()->Disentangle();