Convert Site Isolation Win layout tests to run with --site-per-process.

scripts/slave/recipes/chromium.expected/full_chromium_fyi_Site_Isolation_Win.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 326 matching lines @@
       "/path/to/tmp/json",
       "--test-results-server",
       "test-results.appspot.com",
       "--build-number",
       "571",
       "--builder-name",
       "Site Isolation Win",
       "--step-name",
       "webkit_tests",
       "--additional-driver-flag",
-      "--isolate-sites-for-testing=*.is",
+      "--site-per-process",
       "--additional-expectations",
-      "src\\third_party\\WebKit\\LayoutTests\\FlagExpectations\\isolate-extensions",
+      "src\\third_party\\WebKit\\LayoutTests\\FlagExpectations\\site-per-process",
       "--master-name",
       "chromium.fyi",
       "--debug-rwt-logging"
     ],
     "cwd": "[BUILDER_CACHE]\\Site_Isolation_Win",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
     },
     "name": "webkit_tests",
     "~followup_annotations": [
@@ skipping 41 matching lines @@
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
     },
     "name": "process_dumps"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]