Use FrameIsAd to decide whether to isolate a frame in TopDocumentIsolation mode.

content/public/browser/content_browser_client.cc

Index: content/public/browser/content_browser_client.cc
diff --git a/content/public/browser/content_browser_client.cc b/content/public/browser/content_browser_client.cc
index e32549dda7db35e682f830e735fc7071033eb7ff..7675801876e40bfb099cda2265774f4291fdac63 100644
--- a/content/public/browser/content_browser_client.cc
+++ b/content/public/browser/content_browser_client.cc
@@ -91,11 +91,13 @@ bool ContentBrowserClient::ShouldAllowOpenURL(SiteInstance* site_instance,
   return true;
 }
 
-bool ContentBrowserClient::
-    ShouldFrameShareParentSiteInstanceDespiteTopDocumentIsolation(
-        const GURL& url,
-        SiteInstance* parent_site_instance) {
-  return false;
+bool ContentBrowserClient::ShouldIsolateFrameForTopDocumentIsolation(
+    NavigationHandle* navigation_handle,
+    SiteInstance* main_frame_site_instance) {
+  // In absence of customizations above //content layer, TDI mode should isolate
+  // all cross-site frames.  Additionally, isolating all cross-site frames makes
+  // it easier to test TopDocumentIsolation in content_browsertests.
+  return true;
 }
 
 bool ContentBrowserClient::IsSuitableHost(RenderProcessHost* process_host,