The browser process sends the resource loading hints to the render process at the time of Navigation finish (https://cs.chromium.org/chromium/src/chrome/browser/previews/resource_loading_hints/resource_loading_hints_web_contents_observer.cc?rcl=4fe547befb93a2a29889788c85de80a34656b4a3&l=37).

However, that may be a bit too late to capture loading of all subresources. It's possible that the renderer may have already loaded some of the subresources that were meant to be blocked. 

We should add an additional path to send the hints as soon as the commit happens on the render side.  Approac in https://cs.chromium.org/chromium/src/components/subresource_filter/content/renderer/subresource_filter_agent.cc?rcl=d1c8127a71843a422e1a62ecd2c5b0f09a3dfb3e&l=70 looks promising.