[iOS] Improve readability for GAIA refresh logic.

Currently it is difficult to understand that the GAIA refresh logic only
triggers for the google.com domain. This patch adds a comment to this
effect and ensures that only Google domain URLs are processed when
executing a navigation.

Bug: 1131027
Change-Id: Iebdbd804ef378ce48dda95be98de3ed76c9642d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435184Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813656}

components/signin/ios/browser/account_consistency_service.mm

@@ -151,6 +151,14 @@ void AccountConsistencyHandler::ShouldAllowResponse(
   if (signin::IsUrlEligibleForMirrorCookie(url)) {
     account_consistency_service_->SetChromeConnectedCookieWithUrls(
         {url, GURL(kGoogleUrl)});
+  }
+
+  // Chrome monitors GAIA cookies when navigating to a google.com domain to
+  // ensure that signed-in users remain signed-in to their Google services on
+  // the web. This includes redirects to accounts.google.com.
+  if (google_util::IsGoogleDomainUrl(
+          url, google_util::ALLOW_SUBDOMAIN,
+          google_util::DISALLOW_NON_STANDARD_PORTS)) {
     account_consistency_service_->SetGaiaCookiesIfDeleted();
   }