Report WebGPU CTS JS time

Adds the duration of WebGPU CTS tests to the payload sent
to the test harness so that it can be reported to ResultDB.

Bug: chromium:1336333
Change-Id: I06e16be2c51807c8fbe37730008ed2bd68f82f6c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94520
Auto-Submit: Brian Sheedy <bsheedy@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

webgpu-cts/test_runner.js

@@ -89,7 +89,8 @@ async function runCtsTest(query, use_worker) {
         let isFinal = index == arr.length - 1;
         socket.send(JSON.stringify({'s': res.status,
                                     'l': piece,
-                                    'final': isFinal}));
+                                    'final': isFinal,
+                                    'js_duration_ms': res.timems}));
       });
     };
     await wpt_fn();