Navigation: Replace hardcoded kAboutBlankURL checks with IsAboutBlank().

This is to use the more reliable GURL::IsAboutBlank() when checking for
blank pages instead of just matching the urls.

Change-Id: Ieb5692cf1da8e323baa2e72285d2801d2fc0d1ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583786
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Mohamed Abdelhalim <zetamoo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654066}

content/browser/site_instance_impl.cc

diff --git a/content/browser/site_instance_impl.cc b/content/browser/site_instance_impl.cc
index 6bb834f7..ca5571f 100644
--- a/content/browser/site_instance_impl.cc
+++ b/content/browser/site_instance_impl.cc
@@ -86,7 +86,7 @@
 bool SiteInstanceImpl::ShouldAssignSiteForURL(const GURL& url) {
   // about:blank should not "use up" a new SiteInstance.  The SiteInstance can
   // still be used for a normal web site.
-  if (url == url::kAboutBlankURL)
+  if (url.IsAboutBlank())
     return false;
 
   // The embedder will then have the opportunity to determine if the URL
@@ -453,8 +453,7 @@
 
   // If the destination url is just a blank page, we treat them as part of the
   // same site.
-  GURL blank_page(url::kAboutBlankURL);
-  if (dest_url == blank_page)
+  if (dest_url.IsAboutBlank())
     return true;
 
   // If the source and destination URLs are equal excluding the hash, they have