Bug 1432949 - Return error if channel cannot be opened. Expand download blob test case r=geckoview-reviewers,snorp

Differential Revision: https://phabricator.services.mozilla.com/D75687

mobile/android/geckoview/src/androidTest/assets/www/download.html

@@ -6,11 +6,13 @@
     <script>
       const blob = new Blob(["Downloaded Data"], {type: "text/plain"});
       const element = document.createElement("a");
-      element.href = URL.createObjectURL(blob);
+      const uri = URL.createObjectURL(blob);
+      element.href = uri;
       element.download = "download.txt";
       element.style.display = "none";
       document.body.appendChild(element);
       element.click();
+      URL.revokeObjectURL(uri);
     </script>
   </body>
 </html>

widget/android/WebExecutorSupport.cpp

@@ -414,9 +414,7 @@ nsresult WebExecutorSupport::CreateStreamLoader(
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Finally, open the channel
-  rv = channel->AsyncOpen(listener);
-
-  return NS_OK;
+  return channel->AsyncOpen(listener);
 }
 
 void WebExecutorSupport::Fetch(jni::Object::Param aRequest, int32_t aFlags,