[DevTools] fix: always send a response to fetch-file request in the extension (#34235)

This fixes the displaying of "rendered by" section if owner stacks
contained any native frames. This regressed after
https://github.com/facebook/react/pull/34185, where we added the
Suspense boundary for the StackTraceView.

This fails because the Promise that is responsible for symbolication of
the source is never getting resolved or rejected.
Previously, we would just throw an Error without sending a corresponding
message to the `main` script, and it would just cache a Promise that is
never resolved, hence the Suspense boundary for "rendered by" section is
never resolved.

In a separate change, I think we need to update StackTraceView component
to display `native` as location, instead of `:0`:
<img width="712" height="118" alt="Screenshot 2025-08-20 at 00 20 42"
src="https://github.com/user-attachments/assets/c79735c9-fdd2-467c-96cd-2bc29d38c4e0"
/>

packages/react-devtools-extensions/src/background/messageHandlers.js

@@ -46,14 +46,17 @@ export function handleDevToolsPageMessage(message) {
         payload: {tabId, url},
       } = message;
 
-      if (!tabId) {
-        throw new Error("Couldn't fetch file sources: tabId not specified");
-      }
-
-      if (!url) {
-        throw new Error("Couldn't fetch file sources: url not specified");
-      }
-
+      if (!tabId || !url) {
+        // Send a response straight away to get the Promise fulfilled.
+        chrome.runtime.sendMessage({
+          source: 'react-devtools-background',
+          payload: {
+            type: 'fetch-file-with-cache-error',
+            url,
+            value: null,
+          },
+        });
+      } else {
         chrome.tabs.sendMessage(tabId, {
           source: 'devtools-page',
           payload: {
@@ -61,6 +64,7 @@ export function handleDevToolsPageMessage(message) {
             url,
           },
         });
+      }
 
       break;
     }