prompted by internal thread discussing clean ups after vsync aligned input, which has shipped everywhere except webview. Can we do something about webview, especially to not block any optimizations enabled by these follow up changes :)

Restrictions on webview, both due to apps can directly call WebView.onTouchEvent with synthetic events:
1) We can't enable unbuffered input (call View.requestUnbufferedDispatch) on the webview. I don't know what would happen when that's called on a "fake" events that's not actually from the window..
2) Unaligned input is always a possibility, ie app can call onTouchEvent whenever it likes.

Is there downside to using the buffered input path in chromium even if input is already buffered by android already?

Assuming no to that question, then I'm willing to bet apps won't care if we buffer synthetic events for another frame if input arrived after begin frame. So we could just try enabling this and see if anyone complains.