Bug 1941006 - [devtools] Fix DevTools when debugging a page with an extension document used in an iframe. r=jdescottes,devtools-reviewers

Bug 1214658 hacks the content script sandboxes to used them for iframes loading
extension documents. These documents expect the privileged chrome/browser APIs,
which are exposed by spawning a content script sandboxes.
These sandboxes won't have any metadata as they don't really are content scripts.
These sandboxes won't execute any script.
They will only be used to expose chrome/browser APIs to these iframes.

Differential Revision: https://phabricator.services.mozilla.com/D234824

Author: ochameau

devtools/client/webconsole/test/browser/browser_webconsole_webextension_content_script.js

@@ -23,9 +23,19 @@ add_task(async function () {
 
     files: {
       "content-script.js": function () {
+        /* global browser */
         console.log("def");
+
+        // Create an iframe with a privileged document of the extension
+        const iframe = document.createElement("iframe");
+        iframe.src = browser.runtime.getURL(`iframe.html`);
+        document.body.appendChild(iframe);
+
         Promise.reject("abc");
       },
+
+      "iframe.html": `<div>Extension iframe</div> <script src="iframe.js"></script>`,
+      "iframe.js": `console.log("iframe log"); throw new Error("iframe exception")`,
     },
   });
 
@@ -37,6 +47,13 @@ add_task(async function () {
   await checkUniqueMessageExists(hud, "uncaught exception: abc", ".error");
   await checkUniqueMessageExists(hud, "def", ".console-api");
 
+  await checkUniqueMessageExists(hud, "iframe log", ".console-api");
+  await checkUniqueMessageExists(
+    hud,
+    "Uncaught Error: iframe exception",
+    ".error"
+  );
+
   // Enable the content script preference in order to see content scripts messages,
   // sources and target.
   const onTargetProcessed = waitForTargetProcessed(

devtools/server/connectors/js-process-actor/target-watchers/content_script.sys.mjs

@@ -131,7 +131,10 @@ function createTargetsForWatcher(watcherDataObject, _isProcessActorStartup) {
   const sandboxes = lazy.ExtensionContent.getAllContentScriptGlobals();
   for (const contentScriptSandbox of sandboxes) {
     const metadata = Cu.getSandboxMetadata(contentScriptSandbox);
-    if (metadata["browser-id"] != browserId) {
+    // Ignore sandboxes without metadata which are related to the hack
+    // of bug 1214658, which spawns content script sandboxes in order
+    // to expose chrome/browser API to iframes loading extension documents.
+    if (!metadata || metadata["browser-id"] != browserId) {
       continue;
     }
     createContentScriptTargetActor(watcherDataObject, {