This directory contains code used by WebView and WebContent[1] of iOS Blink to inject javascript from the browser to the renderer, as well as a simple message port style API.
As there is not an iOS builder blocking CQ, it is recommended to manually trigger an ios-blink-rel-fyi trybot job when making changes to detect breakages.
[1] https://source.chromium.org/chromium/chromium/src/+/main:ios/web/content/js_messaging/