Update link from KenjiBaheux/portals to point at the root of WICG/portals.

Change-Id: I6f21ff35ef36e908da88356223a52b413e8b93ca
Reviewed-on: https://chromium-review.googlesource.com/c/1372717Reviewed-by: Lucas Gadani <lfg@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615725}

third_party/blink/renderer/core/html/portal/html_portal_element.h

@@ -21,9 +21,7 @@ class ScriptState;
 // element can be used to embed another top-level browsing context, which can be
 // activated using script. The portal element is still under development and not
 // part of the HTML standard. It can be enabled by passing
-// --enable-features=Portals. See
-// https://github.com/KenjiBaheux/portals/blob/master/explainer.md for more
-// details.
+// --enable-features=Portals. See also https://github.com/WICG/portals.
 class CORE_EXPORT HTMLPortalElement : public HTMLFrameOwnerElement {
   DEFINE_WRAPPERTYPEINFO();