test,inspector: add heap allocation tracker test

This provides coverage for the `InspectorTimer` instances
created as part of heap allocation tracking.

PR-URL: #26089
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-inspector-heap-allocation-tracker.js

@@ -0,0 +1,46 @@
+'use strict';
+const common = require('../common');
+
+common.skipIfInspectorDisabled();
+
+const assert = require('assert');
+const inspector = require('inspector');
+const stream = require('stream');
+const { Worker, workerData } = require('worker_threads');
+
+const session = new inspector.Session();
+session.connect();
+session.post('HeapProfiler.enable');
+session.post('HeapProfiler.startTrackingHeapObjects',
+             { trackAllocations: true });
+
+// Perform some silly heap allocations for the next 100 ms.
+const interval = setInterval(() => {
+  new stream.PassThrough().end('abc').on('data', common.mustCall());
+}, 1);
+
+setTimeout(() => {
+  clearInterval(interval);
+
+  // Once the main test is done, we re-run it from inside a Worker thread
+  // and stop early, as that is a good way to make sure the timer handles
+  // internally created by the inspector are cleaned up properly.
+  if (workerData === 'stopEarly')
+    process.exit();
+
+  let data = '';
+  session.on('HeapProfiler.addHeapSnapshotChunk',
+             common.mustCallAtLeast((event) => {
+               data += event.params.chunk;
+             }));
+
+  // TODO(addaleax): Using `{ reportProgress: true }` crashes the process
+  // because the progress indication event would mean calling into JS while
+  // a heap snapshot is being taken, which is forbidden.
+  // What can we do about that?
+  session.post('HeapProfiler.stopTrackingHeapObjects');
+
+  assert(data.includes('PassThrough'), data);
+
+  new Worker(__filename, { workerData: 'stopEarly' });
+}, 100);