According to a work in progress Chromium source code commit, Google Chrome might get a "Never-Slow Mode" flag in the future which, when enabled, would block the loading of website resources that exceed a pre-defined size limit.

As detailed in Alex Russell's not yet reviewed "Never-Slow Mode" commit, the new Chrome flag will "enforce per-interaction budgets designed to keep the main thread clean (design doc currently internal)."

To be more exact, Russell's Chromium work-in-progress commit will add the following:

Adds `--enable-features=NeverSlowMode` to enforce per-interaction budgets designed to keep the main thread clean (design doc currently internal). Currently blocks large scripts, sets budgets for certain resource types (script, font, css, images), turns off document.write(), clobbers sync XHR, enables client-hints pervasively, and buffers resources without `Content-Length` set. Budgets are re-set on interaction (click/tap/scroll). Long script tasks (> 200ms) pause all page execution until next interaction. Caps do not apply to workers and size caps are lifted for resources loaded from Service Worker Cache Storage. Current caps; all values are wire (transfer/compressed) size:

Additionally, the size caps set in place by a possible "Never-Slow Mode" flag will not apply to workers and they will also not be for resources which will be loaded from Service Worker Cache Storage.

This new flag which is still in an incipient development state (the author calls it a prototype in the commit log), will make sure that websites do not assault the browser with large-sized resources hammering down performance and speed once implemented and enabled.

Furthermore, according to the WIP commit status description, "This change isn't ready to be reviewed or submitted. It will not appear in dashboards and email notifications will be silenced until the review is started."

The current caps the flag is designed to enforce are:

Per-image max size: 1MiB

Total image budget: 2MiB

Per-stylesheet max size: 100KiB

Total stylesheet budget: 200KiB

Per-script max size: 50KiB

Total script budget: 500KiB

Per-font max size: 100KiB

Total font budget: 100KiB

Total connection limit: 10

Long-task limit: 200ms

The source code attached to the prototype "Never-Slow Mode" flag commit also exposes what the flag will do: "Enables an experimental browsing mode that restricts resource loading and runtime processing to deliver a consistently fast experience."

However, Russell also warns that enabling it may also silently break website content given that some resources might get blocked and break site functionality.

Never-Slow Mode flag description

H/T Chrome Story