Add type to CTS runner message

Adds the "type" field to the websocket message sent
by the CTS JavaScript code with a value of
"TEST_FINISHED". This is in preparation for the
switch to using a heartbeat system for test timeouts
instead of a fixed timeout.

Bug: chromium:1340602
Change-Id: I886d89dbdfb1e3946dd8c59ecf23f9b18385b65e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/97280
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@google.com>
Auto-Submit: Brian Sheedy <bsheedy@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

webgpu-cts/test_runner.js

@@ -90,7 +90,8 @@ async function runCtsTest(query, use_worker) {
         socket.send(JSON.stringify({'s': res.status,
                                     'l': piece,
                                     'final': isFinal,
-                                    'js_duration_ms': res.timems}));
+                                    'js_duration_ms': res.timems,
+                                    'type': 'TEST_FINISHED'}));
       });
     };
     await wpt_fn();