As @davidsgrogan noticed in this comment, for transferred size, the spec says:

If the item has a preferred aspect ratio and its computed cross size property is definite

In 9.8, the definite rule says:

the outer cross size of any stretched flex items ... is considered definite.

Should the stretched definite cross size be used in computing transferred size? Or in other words, should the transferred size defined as If the item has a preferred aspect ratio and a definite cross size, then ...? (similar to the flex algo 3B where a definite cross size is used to compute flex base size)

Consider the following example:

<div style="display:flex; width:0; height: 50px;">
  <img style="" src="https://placehold.it/300x100" >
</div>

It's obvious that the image has no specified size suggestion and the content size suggestion is 300px. Currently Firefox Nightly gives the image 150px width as it does use definite cross size and aspect-ratio to compute to transferred size. Chrome and Safari gives the image 300px width. (I guess both implementations think the image has no transferred size.)

cc @tabatkins @dholbert