[omt-worker-fetch] add upgrade-insecure-requests/mixed-content and refine

This CL:
- Adds wpt/upgrade-insecure-requests and worker-related
  subdirectories of wpt/mixed-content.
- Fixes the runtime flags for external/wpt/referrer-policy.
- Merges multiple README.txt into a single top-level README.md.
- Updates README.md to mention classic shared workers.

Bug: 835717, 924041
Change-Id: Ifbafe9ca89a0c45d99e23d295430df89125d71ce
Reviewed-on: https://chromium-review.googlesource.com/c/1389639Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629457}

third_party/blink/web_tests/TestExpectations

@@ -4192,6 +4192,7 @@ crbug.com/636055 external/wpt/css/css-multicol/multicol-span-all-margin-nested-0
 crbug.com/792446 external/wpt/css/css-multicol/multicol-span-float-001.xht [ Failure ]
 
 crbug.com/917554 external/wpt/upgrade-insecure-requests/worker-subresource-fetch-upgrade.https.html [ Crash ]
+crbug.com/917554 virtual/omt-worker-fetch/external/wpt/upgrade-insecure-requests/worker-subresource-fetch-upgrade.https.html [ Crash ]
 
 # Different results on try bots and CQ, skipped to unblock wpt import.
 crbug.com/888443 external/wpt/css/cssom-view/scroll-behavior-default-css.html [ Skip ]

third_party/blink/web_tests/VirtualTestSuites

@@ -664,10 +664,35 @@
     "base": "external/wpt/service-workers/service-worker",
     "args": ["--disable-features=ServiceWorkerServicification,NetworkService"]
   },
+  {
+    "prefix": "omt-worker-fetch",
+    "base": "external/wpt/mixed-content/classic-data-worker-fetch",
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch,NetworkService"]
+  },
+  {
+    "prefix": "omt-worker-fetch",
+    "base": "external/wpt/mixed-content/module-data-worker-import",
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch,NetworkService"]
+  },
+  {
+    "prefix": "omt-worker-fetch",
+    "base": "external/wpt/mixed-content/module-worker-top-level",
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch,NetworkService"]
+  },
+  {
+    "prefix": "omt-worker-fetch",
+    "base": "external/wpt/mixed-content/worker-request",
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch,NetworkService"]
+  },
   {
     "prefix": "omt-worker-fetch",
     "base": "external/wpt/referrer-policy",
-    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch"]
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch,NetworkService"]
+  },
+  {
+    "prefix": "omt-worker-fetch",
+    "base": "external/wpt/upgrade-insecure-requests",
+    "args": ["--enable-features=OffMainThreadDedicatedWorkerScriptFetch,OffMainThreadSharedWorkerScriptFetch,NetworkService"]
   },
   {
     "prefix": "omt-worker-fetch",

third_party/blink/web_tests/virtual/omt-worker-fetch/external/wpt/referrer-policy/README.txt → third_party/blink/web_tests/virtual/omt-worker-fetch/README.md

-This directory is for testing off-the-main-thread top-level worker classic
-script loading. See https://crbug.com/835717.
+This directory is for testing off-the-main-thread top-level worker script
+loading for
+
+- [Classic dedicated workers](https://crbug.com/835717) and
+- [Classic shared workers](https://crbug.com/924041).

third_party/blink/web_tests/virtual/omt-worker-fetch/external/wpt/workers/README.txt

-This directory is for testing off-the-main-thread top-level worker classic
-script loading. See https://crbug.com/835717.

third_party/blink/web_tests/virtual/omt-worker-fetch/fast/workers/README.txt

-This directory is for testing off-the-main-thread top-level worker classic
-script loading. See https://crbug.com/835717.

third_party/blink/web_tests/virtual/omt-worker-fetch/http/tests/workers/README.txt

-This directory is for testing off-the-main-thread top-level worker classic
-script loading. See https://crbug.com/835717.