shill: add MockIcmpSession, IcmpSessionFactory, and MockIcmpSessionFactory

Add MockIcmpSession class that allows for mocking of
IcmpSession function calls. Add an IcmpSessionFactory and
a corresponding Mock of this factory to allow IcmpSessions
that are dynamically allocated within a class implementation
to be mocked in unit tests.

A forthcoming CL will use these classes for testing.

BUG=None
TEST=Compiling shill for unit tests succeeds.

Change-Id: Ic327a19229d25146abf62f2228782b1826b186e7
Reviewed-on: https://chromium-review.googlesource.com/289954
Tested-by: Samuel Tan <samueltan@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Samuel Tan <samueltan@chromium.org>
diff --git a/mock_icmp_session.cc b/mock_icmp_session.cc
new file mode 100644
index 0000000..8c1595a
--- /dev/null
+++ b/mock_icmp_session.cc
@@ -0,0 +1,14 @@
+// Copyright 2015 The Chromium OS 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 "shill/mock_icmp_session.h"
+
+namespace shill {
+
+MockIcmpSession::MockIcmpSession(EventDispatcher* dispatcher)
+    : IcmpSession(dispatcher) {}
+
+MockIcmpSession::~MockIcmpSession() {}
+
+}  // namespace shill