Add StaleWhileRevalidateExperiment histograms.

net/base/stale_while_revalidate_experiment_domains.h

Index: net/base/stale_while_revalidate_experiment_domains.h
diff --git a/net/base/stale_while_revalidate_experiment_domains.h b/net/base/stale_while_revalidate_experiment_domains.h
new file mode 100644
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+++ b/net/base/stale_while_revalidate_experiment_domains.h
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+// Copyright 2015 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.
+
+#ifndef NET_BASE_STALE_WHILE_REVALIDATE_EXPERIMENT_DOMAINS_H_
+#define NET_BASE_STALE_WHILE_REVALIDATE_EXPERIMENT_DOMAINS_H_
+
+#include "base/strings/string_piece.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+// Returns true if |host| matches one of the domains of interest for
+// stale-while-revalidate histograms. If "example.com" was in the list, then
+// "example.com" would match, as would "www.example.com" and "a.b.example.com",
+// but not "com" or "an-example.com". Trailing '.' characters on |host| are
+// ignored. |host| is expected to be canonicalised to lowercase (as performed by
+// GURL).
+// TODO(ricea): Remove this in April 2016 or before. crbug.com/348877
+NET_EXPORT bool IsHostInStaleWhileRevalidateExperimentDomain(
+    const base::StringPiece& host);
+
+}  // namespace net
+
+#endif  // NET_BASE_STALE_WHILE_REVALIDATE_EXPERIMENT_DOMAINS_H_