[WPT/common/security-features] Make subresourceContext unmodified

To enable to reference `sourceContextList` when checking results.

Bug: 906850
Change-Id: I6d27ac081cef1f2cfa3d387a2a448833aa424694
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1725258
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683371}

third_party/blink/web_tests/external/wpt/common/security-features/resources/common.js

@@ -1104,7 +1104,7 @@ self.invokeRequest = invokeRequest;
 */
 function invokeFromWorker(isDataUrl, workerOptions,
                           subresource, sourceContextList) {
-  const currentSourceContext = sourceContextList.shift();
+  const currentSourceContext = sourceContextList[0];
   let workerUrl =
     "/common/security-features/scope/worker.py?policyDeliveries=" +
     encodeURIComponent(JSON.stringify(
@@ -1128,7 +1128,7 @@ function invokeFromWorker(isDataUrl, workerOptions,
     .then(url => {
       const worker = new Worker(url, workerOptions);
       worker.postMessage({subresource: subresource,
-                          sourceContextList: sourceContextList});
+                          sourceContextList: sourceContextList.slice(1)});
       return bindEvents2(worker, "message", worker, "error", window, "error");
     })
     .then(event => {
@@ -1139,7 +1139,7 @@ function invokeFromWorker(isDataUrl, workerOptions,
 }
 
 function invokeFromIframe(subresource, sourceContextList) {
-  const currentSourceContext = sourceContextList.shift();
+  const currentSourceContext = sourceContextList[0];
   const frameUrl =
     "/common/security-features/scope/document.py?policyDeliveries=" +
     encodeURIComponent(JSON.stringify(
@@ -1165,7 +1165,7 @@ function invokeFromIframe(subresource, sourceContextList) {
                   window, "message", iframe, "error", window, "error");
               iframe.contentWindow.postMessage(
                   {subresource: subresource,
-                   sourceContextList: sourceContextList},
+                   sourceContextList: sourceContextList.slice(1)},
                   "*");
               return promise;
             })