fix: Handle error when offscreen document already exists

A `try..catch` block has been added to catch errors about the Offscreen
document already existing. This circumstance is not a bug, it's
expected to happen sometimes due to race conditions between
`hasDocument` and the creation step. The code in question is just meant
to create the document if it doesn't exist, so it's OK if we get this
error.

The `hasDocument` call has been removed as well, since it's now
redundant. This function wasn't safe to call anyway; it's an
undocumented private function.

See here for more information:
* https://stackoverflow.com/a/7725839
* https://groups.google.com/a/chromium.org/g/chromium-extensions/c/D5Jg2ukyvUc4

Fixes #25118

app/scripts/offscreen.js

@@ -9,29 +9,49 @@ import { OffscreenCommunicationTarget } from '../../shared/constants/offscreen-c
  */
 export async function createOffscreen() {
   const { chrome } = globalThis;
-  if (!chrome.offscreen || (await chrome.offscreen.hasDocument())) {
+  if (!chrome.offscreen) {
     return;
   }
 
+  let offscreenDocumentLoadedListener;
   const loadPromise = new Promise((resolve) => {
-    const messageListener = (msg) => {
+    offscreenDocumentLoadedListener = (msg) => {
       if (
         msg.target === OffscreenCommunicationTarget.extensionMain &&
         msg.isBooted
       ) {
-        chrome.runtime.onMessage.removeListener(messageListener);
+        chrome.runtime.onMessage.removeListener(
+          offscreenDocumentLoadedListener,
+        );
         resolve();
       }
     };
-    chrome.runtime.onMessage.addListener(messageListener);
+    chrome.runtime.onMessage.addListener(offscreenDocumentLoadedListener);
   });
 
-  await chrome.offscreen.createDocument({
-    url: './offscreen.html',
-    reasons: ['IFRAME_SCRIPTING'],
-    justification:
-      'Used for Hardware Wallet and Snaps scripts to communicate with the extension.',
-  });
+  try {
+    await chrome.offscreen.createDocument({
+      url: './offscreen.html',
+      reasons: ['IFRAME_SCRIPTING'],
+      justification:
+        'Used for Hardware Wallet and Snaps scripts to communicate with the extension.',
+    });
+  } catch (error) {
+    if (
+      error?.message?.startsWith(
+        'Only a single offscreen document may be created',
+      )
+    ) {
+      console.debug('Offscreen document already exists; skipping creation');
+      if (offscreenDocumentLoadedListener) {
+        chrome.runtime.onMessage.removeListener(
+          offscreenDocumentLoadedListener,
+        );
+      }
+      return;
+    }
+    throw error;
+  }
 
   // In case we are in a bad state where the offscreen document is not loading, timeout and let execution continue.
   const timeoutPromise = new Promise((resolve) => {