Worker: Enable UseCounter for SharedWorkerGlobalScope

third_party/WebKit/LayoutTests/fast/workers/resources/shared-worker-usecounter.js

+onconnect = e => {
+  var port = e.ports[0];
+  port.onmessage = () => {
+    // Call fetch() just for recording API use.
+    fetch('notfound').catch(() => port.postMessage('fetched'));

[Rick Byers, 2017/01/26 03:02:37]

please use a feature which is Deprecated (or even one of each).  I think you're
going to hit a DCHECK for the deprecated case (since UseCounter.cpp today
doesn't expect deprecated features to come through the normal path).  Perhaps we
should just relax that DCHECK if there's not an easy way to separate this case
out...

[nhiroki, 2017/01/27 16:58:16]

You're right! Calling a deprecated feature hits DCHECK. Instead of relaxing the
check, the latest patchset ccheck whether a given feature is deprecated and
calls countDeprecate in the case. See
SharedWorkerRepositoryClientImpl.cpp::countFeature.

+  };
+  port.postMessage('connected');
+}