Adds a MerkleAuditProof struct to net/cert.

net/cert/merkle_audit_proof_unittest.cc

+// Copyright 2016 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 "net/cert/merkle_audit_proof.h"
+
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace net {
+namespace ct {
+namespace {
+
+TEST(MerkleAuditProofTest, CalculatesAuditPathLengthCorrectly) {
+  EXPECT_EQ(20u, CalculateAuditPathLength(123456, 999999));

[Eran Messeri, 2016/05/23 13:10:52]

Add a few more test cases, particularly relating to where the node in the tree
is?

[Rob Percival, 2016/05/24 17:10:05]

Done.

+}
+
+}  // namespace
+}  // namespace ct
+}  // namespace net