Electron Releases

Description of Change

A renderer's network requests and file:// loads no longer wait for the main process's JavaScript. Today every URLLoaderFactory Electron hands a renderer is fronted by objects bound on the browser UI thread, so each <script>, stylesheet, fetch() or image request is dispatched by the main thread and sits in its queue while app code runs. Measured on Linux x64 release builds, medians of 3 warm loads, with the main process either idle or running 100 ms of JavaScript right after the navigation commits (which is what app startup looks like from the window's side):

Four commits, each independent:

1. Keep renderer network requests off the main thread unless they are observed. WillCreateURLLoaderFactory wrapped every factory in a ProxyingURLLoaderFactory on the UI thread, listeners or not. Renderer-facing factories now get a small URLLoaderFactoryGate on the IO thread in front of the proxy: it forwards straight to the network service unless the session has a webRequest listener, an intercepted scheme matching the request, or an --ignore-connections-limit domain, in which case the request goes to the proxy exactly as before. That state is a few words under a lock that api::WebRequest and ProtocolRegistry update, so a listener added at any time applies to the next request without recreating factories (listeners re-run on redirects, which is why their URL filters are not applied at the gate). With a listener registered nothing changes, within noise.
2. Bind the file:// URL loader factory off the main thread. AsarURLLoaderFactory only posts loaders to the thread pool, so it is now bound on the IO thread; file:// subresources stop queueing behind main-process work.
3. Skip the trusted-header round trips for requests proxied without webRequest listeners. The proxy put every request in "extraHeaders" mode (two TrustedHeaderClient round trips per request); that is what lets listeners see and modify network-owned headers, so it stays whenever the session has any webRequest listener, and requests that reach the proxy only for an intercepted protocol or an --ignore-connections-limit domain skip it.
4. Don't build console-message events while nothing listens for them. OnDidAddMessageToConsole created an event object and emitted into JS for every renderer console call; WebContents now keeps a flag from newListener/removeListener and returns early without it.

Checklist

• PR description included and stakeholders cc'd
• npm test passes (webRequest, protocol, session, net, BrowserWindow, webContents, asar, webview, subframe, service worker, extensions and chromium specs locally on Linux)
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.
• I have reviewed and verified the changes

Release Notes

Notes: Page resources, fetch() calls and file:// loads in renderers no longer wait for the main process to be idle when no webRequest listeners or protocol interceptors are registered.