Reporting: Implement cache.

net/reporting/reporting_test_util.h

+// 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.
+
+#ifndef NET_REPORTING_REPORTING_TEST_UTIL_H_
+#define NET_REPORTING_REPORTING_TEST_UTIL_H_
+
+#include "net/reporting/reporting_cache.h"
+#include "url/gurl.h"
+#include "url/origin.h"
+
+namespace net {
+
+// Finds a particular client (by origin and endpoint) in the cache and returns
+// it (or nullptr if not found).
+const ReportingCache::Client* FindClientInCache(const ReportingCache* cache,
+                                                const url::Origin& origin,
+                                                const GURL& endpoint);
+
+}  // namespace net
+
+#endif  // NET_REPORING_REPORTING_TEST_UTIL_H_