Revert "Revert "[css-typed-om] Ensure StylePropertyMapReadonly IDL ma…

…tches spec.""

This reverts commit 35bfb10373c5b34c193ad9a7c569d6aa429028fc.

Reason for revert: Trying to reland.

Original change's description:
> Revert "[css-typed-om] Ensure StylePropertyMapReadonly IDL matches spec."
>
> This reverts commit 43700726a48ebedf10af437c644ec46d862fb46b.
>
> Reason for revert: Causes build failure on Google Chrome ChromeOS:
> https://ci.chromium.org/buildbot/chromium.chrome/Google%20Chrome%20ChromeOS/45929
>
> Original change's description:
> > [css-typed-om] Ensure StylePropertyMapReadonly IDL matches spec.
> >
> > Spec added a new .size member, which we implement in this patch.
> >
> > Bug: 812915
> > Change-Id: Ib48fc7b8053c41e4c79dc9cc280bc18376e5fbe0
> > Reviewed-on: https://chromium-review.googlesource.com/930101
> > Reviewed-by: nainar <nainar@chromium.org>
> > Commit-Queue: Darren Shen <shend@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#538304}
>
> TBR=nainar@chromium.org,shend@chromium.org
>
> Change-Id: I442aebc331ddc97c09c870299ab0ab76f5ce7773
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 812915
> Reviewed-on: https://chromium-review.googlesource.com/930179
> Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
> Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#538309}

Bug: 812915
Change-Id: Ia45bc81d58a807448e00d21a33c97e2210712bb2

interfaces/css-typed-om.idl

@@ -7,13 +7,13 @@ interface CSSStyleValue {
 
 [Exposed=(Window, Worker, PaintWorklet, LayoutWorklet)]
 interface StylePropertyMapReadOnly {
-    readonly maplike<DOMString, sequence<CSSStyleValue>>;
+    iterable<DOMString, sequence<CSSStyleValue>>;
     any get(DOMString property);
     /* 'any' means (undefined or CSSStyleValue) here,
        see https://github.com/heycam/webidl/issues/60 */
     sequence<CSSStyleValue> getAll(DOMString property);
     boolean has(DOMString property);
-    stringifier;
+    readonly attribute long size;
 };
 
 callback UpdateFunction = CSSStyleValue (CSSStyleValue oldValue);