Add WPT for denormal behavior in AudioWorkletGlobalScope

Currently Chrome's JS execution in AudioWorkletGlobalScope does not
handle the denormals properly. To make this clear, we are adding this
test to keep a reference point for the future discussion.

Bug: 1446038
Test: external/wpt/webaudio/the-audio-api/the-audioworklet-interface/audioworklet-denormals.https.html
Change-Id: If5b51f3eacb1f13d824562cad9e6dba249a0ba96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4590457
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Reviewed-by: Michael Wilson <mjwilson@chromium.org>
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1153539}

webaudio/the-audio-api/the-audioworklet-interface/audioworklet-denormals.https.window.js

@@ -0,0 +1,26 @@
+'use strict';
+
+// Test if the JS code execution in AudioWorkletGlobalScope can handle the
+// denormals properly. For more details, see:
+// https://esdiscuss.org/topic/float-denormal-issue-in-javascript-processor-node-in-web-audio-api
+promise_test(async () => {
+  // In the main thread, the denormals should be non-zeros.
+  assert_not_equals(Number.MIN_VALUE, 0.0,
+                    'The denormals should be non-zeros.');
+
+  const context = new AudioContext();
+  await context.audioWorklet.addModule(
+      './processors/denormal-test-processor.js');
+
+  const denormalTestProcessor = new AudioWorkletNode(context, 'denormal-test');
+
+  return new Promise(resolve => {
+    denormalTestProcessor.port.onmessage = resolve;
+    denormalTestProcessor.connect(context.destination);
+  }).then(event => {
+    // In the AudioWorkletGlobalScope, the denormals should be non-zeros too.
+    assert_true(
+        event.data.result,
+        'The denormals should be non-zeros in AudioWorkletGlobalScope.');
+  });
+}, 'Test denormal behavior in AudioWorkletGlobalScope');

webaudio/the-audio-api/the-audioworklet-interface/processors/denormal-test-processor.js

@@ -0,0 +1,12 @@
+class DenormalTestProcessor extends AudioWorkletProcessor {
+  process() {
+    // The denormals should be non-zeros. Otherwise, it's a violation of
+    // ECMA specification: https://tc39.es/ecma262/#sec-number.min_value
+    this.port.postMessage({
+      result: Number.MIN_VALUE !== 0.0
+    });
+    return false;
+  }
+}
+
+registerProcessor('denormal-test', DenormalTestProcessor);