Add gmock into our dependencies.

third_party/boost/boost/preprocessor/seq/first_n.hpp

Index: third_party/boost/boost/preprocessor/seq/first_n.hpp
diff --git a/third_party/boost/boost/preprocessor/seq/first_n.hpp b/third_party/boost/boost/preprocessor/seq/first_n.hpp
new file mode 100644
index 0000000000000000000000000000000000000000..c3c0716ee7912cbca00de86cd969b904a3ba0ebb
--- /dev/null
+++ b/third_party/boost/boost/preprocessor/seq/first_n.hpp
@@ -0,0 +1,30 @@
+# /* **************************************************************************
+#  *                                                                          *
+#  *     (C) Copyright Paul Mensonides 2002.
+#  *     Distributed under the Boost Software License, Version 1.0. (See
+#  *     accompanying file LICENSE_1_0.txt or copy at
+#  *     http://www.boost.org/LICENSE_1_0.txt)
+#  *                                                                          *
+#  ************************************************************************** */
+#
+# /* See http://www.boost.org for most recent version. */
+#
+# ifndef BOOST_PREPROCESSOR_SEQ_FIRST_N_HPP
+# define BOOST_PREPROCESSOR_SEQ_FIRST_N_HPP
+#
+# include <boost/preprocessor/config/config.hpp>
+# include <boost/preprocessor/control/if.hpp>
+# include <boost/preprocessor/seq/detail/split.hpp>
+# include <boost/preprocessor/tuple/eat.hpp>
+# include <boost/preprocessor/tuple/elem.hpp>
+#
+# /* BOOST_PP_SEQ_FIRST_N */
+#
+# if ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_EDG()
+#    define BOOST_PP_SEQ_FIRST_N(n, seq) BOOST_PP_IF(n, BOOST_PP_TUPLE_ELEM, BOOST_PP_TUPLE_EAT_3)(2, 0, BOOST_PP_SEQ_SPLIT(n, seq (nil)))
+# else
+#    define BOOST_PP_SEQ_FIRST_N(n, seq) BOOST_PP_SEQ_FIRST_N_I(n, seq)
+#    define BOOST_PP_SEQ_FIRST_N_I(n, seq) BOOST_PP_IF(n, BOOST_PP_TUPLE_ELEM, BOOST_PP_TUPLE_EAT_3)(2, 0, BOOST_PP_SEQ_SPLIT(n, seq (nil)))
+# endif
+#
+# endif