Worker: Run more WPTs with PlzDedicatedWorker

This CL enables PlzDedicatedWorker for following tests:

- fast/workers
- wpt/referrer-policy/

Bug: 971173
Change-Id: I2d53323a8c73b9c695b525725c883928459a5896
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1647499Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666605}

third_party/blink/web_tests/VirtualTestSuites

@@ -594,7 +594,7 @@
   {
     "prefix": "omt-worker-fetch",
     "base": "external/wpt/referrer-policy",
-    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadServiceWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch"]
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,PlzDedicatedWorker,OffMainThreadServiceWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch"]
   },
   {
     "prefix": "omt-worker-fetch",
@@ -624,7 +624,7 @@
   {
     "prefix": "omt-worker-fetch",
     "base": "fast/workers",
-    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadServiceWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch"]
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,PlzDedicatedWorker,OffMainThreadServiceWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch"]
   },
   {
     "prefix": "omt-worker-fetch",