Increment encoded/decoded body size for constructed responses (#1664)

Closes w3c/navigation-timing#124

Author: noamr

docs/index.bs

@@ -1640,6 +1640,8 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
                             ::
                                 1. Assert: |chunk| is a {{Uint8Array}}.
                                 1. Append the bytes represented by |chunk| to |bytes|.
+                                1. Increment |potentialResponse|'s [=response/body info=]'s [=response body info/encoded size=] by |bytes|'s {{Uint8Array/size}}.
+                                1. Increment |potentialResponse|'s [=response/body info=]'s [=response body info/decoded size=] by |bytes|'s {{Uint8Array/size}}.
                                 1. Perform ! [=DetachArrayBuffer=](|chunk|.\[[ViewedArrayBuffer]]).
                             : [=read request/close steps=]
                             ::