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_
+
+class GURL;
+
+namespace url {
+class Origin;
+}  // namespace url
+
+namespace net {
+
+class ReportingCache;
+struct ReportingClient;
+
+// Finds a particular client (by origin and endpoint) in the cache and returns
+// it (or nullptr if not found).
+const ReportingClient* FindClientInCache(const ReportingCache* cache,
+                                         const url::Origin& origin,
+                                         const GURL& endpoint);
+
+}  // namespace net
+
+#endif  // NET_REPORING_REPORTING_TEST_UTIL_H_