Does chromium provide a way to use unoptimized render path?

[LD Joker]

My use case may be strange, but I really wanna know if chromium provide some ways to use the unoptimized rendering, just like the picture shows below(come from 

https://developers.google.com/web/fundamentals/performance/critical-rendering-path).

I want chromium to render all the things at once no matter how long it may take. Because in my application I use CEF(chromium embedded framework) to manipulate chromium, I have some JS fronted-end code, which is actually an CSS animation player. And my application is C++ which use CEF to get render data from chromium(by sending devtools protocol Page.captureScreenshot message or use CEF's OnPaint callback). 

The situation is that

(1) I use chromium to load some website page.

(2) After the page is loaded, I execuate JS code to play animation by using seek function to change CSS style in order to achieve animation.

(3) I send chromium devtools protocol to take png screenshots or use CEF's OnPaint callback(that callback will get frame data whenever chromium is finishing rendering one frame) to get the raw rendered data.

(4) I use those data to do some post-processing and finally use ffmpeg to encode so I get a mp4 video file.

But the problem is that after I execuate my JS code to do seeking(which is actually changing the CSS style), the chromium may render several times just like the picture shows below, so the screenshot I get from Page.captureScreenshot protocol may look like a intermediate state. So does the CEF's OnPaint callback, it will get serveral frames.

Ok, anyway I just want to get some suggestion on how to make chromium render all the things at once. Does chromium have such ability?