test: move some fixtures from spec/ to spec-main/ (#21403)

spec-main/fixtures/extensions/content-script/all_frames-preload.js

@@ -0,0 +1,14 @@
+const { ipcRenderer, webFrame } = require('electron')
+
+if (process.isMainFrame) {
+  // https://github.com/electron/electron/issues/17252
+  ipcRenderer.on('executeJavaScriptInFrame', (event, frameRoutingId, code, responseId) => {
+    const frame = webFrame.findFrameByRoutingId(frameRoutingId)
+    if (!frame) {
+      throw new Error(`Can't find frame for routing ID ${frameRoutingId}`)
+    }
+    frame.executeJavaScript(code, false).then(result => {
+      event.sender.send(`executeJavaScriptInFrame_${responseId}`, result)
+    })
+  })
+}