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

chrome/browser/page_load_metrics/observers/ads_detection.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/page_load_metrics/observers/ads_detection.h"
+
+#include "base/strings/string_util.h"
+#include "url/gurl.h"
+
+bool IsAdFrame(base::StringPiece frame_name, const GURL& frame_url) {
+  // Google ads are prevalent and easy to track, so we'll start by tracking
+  // those. Note that the frame name can be very large, so be careful to avoid
+  // full string searches if possible.
+  // TODO(jkarlin): Track other ad networks that are easy to identify.
+
+  if (base::StartsWith(frame_name, "google_ads_iframe",

[Charlie Reis, 2017/06/30 23:28:45]

Sanity check: Any page can trigger TDI by naming its cross-site frame
"google_ads_iframe"?  :)  I suppose false positives aren't a big deal?

[Łukasz Anforowicz, 2017/07/01 00:10:53]

Correct.  Thanks for raising this angle - I honestly haven't thought about this.
I think that yes, false positives aren't a big deal.

+                       base::CompareCase::SENSITIVE) ||
+      base::StartsWith(frame_name, "google_ads_frame",
+                       base::CompareCase::SENSITIVE)) {
+    return true;
+  }
+
+  if (frame_url.host_piece() == "tpc.googlesyndication.com" &&
+      base::StartsWith(frame_url.path_piece(), "/safeframe",
+                       base::CompareCase::SENSITIVE)) {
+    return true;
+  }
+
+  return false;
+}