Expose a filtered content-encoding value to resource timing (#411)

Add text to specify that resourceTiming exposes the new field `content-encoding` in `response body info`.




* Add contentEncoding to resource timing interface.

* contentEncoding must be filtered before being reported.

* improve text.

* Add updated details on how contentEncoding should be filtered.




* Fix and improve contentEncoding steps.

Also applied an improvement at "transferSize".

* Move the "note" to informative note.

* if codings[0] is empty string

It should be returned.

* Update this PR accoridng to the latest fetch spec.

* Remove some superfluous words

Co-authored-by: Anne van Kesteren <[email protected]>

---------

Co-authored-by: Guohui Deng <[email protected]>
Co-authored-by: Anne van Kesteren <[email protected]>

Author: 3 people

index.html

@@ -376,6 +376,7 @@ <h3>
               readonly attribute unsigned short responseStatus;
               readonly attribute RenderBlockingStatusType renderBlockingStatus;
               readonly attribute DOMString contentType;
+              readonly attribute DOMString contentEncoding;
               [Default] object toJSON();
           };
         </pre>
@@ -667,8 +668,7 @@ <h3>
           info</a>'s [=response body info/decoded size=].
         </p>
         <p data-dfn-for="PerformanceResourceTiming">
-          The <dfn>transferSize</dfn> getter steps are to perform the following
-          steps:
+          The <dfn>transferSize</dfn> getter steps are:
         </p>
         <ol>
           <li>
@@ -715,6 +715,11 @@ <h3>
           <a data-for="PerformanceResourceTiming">resource info</a>'s
           [=response body info/content type=].
         </p>
+        <p data-dfn-for="PerformanceResourceTiming">
+          The <dfn>contentEncoding</dfn> getter steps are to return
+          <a>this</a>'s <a data-for="PerformanceResourceTiming">resource info
+          </a>'s [=response body info/content encoding=].
+        </p>
         <p data-dfn-for="PerformanceResourceTiming">
           The <dfn>renderBlockingStatus</dfn> getter steps are to return
           <a data-link-for="RenderBlockingStatusType">blocking</a> if