Keep subdomains of an isolated origin in the isolated origin's SiteInstance.

content/browser/isolated_origin_util.cc

Index: content/browser/isolated_origin_util.cc
diff --git a/content/browser/isolated_origin_util.cc b/content/browser/isolated_origin_util.cc
new file mode 100644
index 0000000000000000000000000000000000000000..811ded12b16e488da3d24594b393fc59b9e28b49
--- /dev/null
+++ b/content/browser/isolated_origin_util.cc
@@ -0,0 +1,27 @@
+// Copyright (c) 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 "content/browser/isolated_origin_util.h"
+
+#include "base/strings/string_util.h"
+#include "url/gurl.h"
+
+namespace content {
+
+// static
+bool IsolatedOriginUtil::DoesOriginMatchIsolatedOrigin(
+    const url::Origin& origin,
+    const url::Origin& isolated_origin) {
+  if (origin.scheme() != isolated_origin.scheme())
+    return false;
+
+  if (origin.port() != isolated_origin.port())
+    return false;
+
+  // Subdomains of an isolated origin are considered to be in the same isolated
+  // origin.
+  return origin.GetURL().DomainIs(isolated_origin.host());
+}
+
+}  // namespace content