Add gmock into our dependencies.

third_party/boost/boost/fusion/support/tag_of_fwd.hpp

Index: third_party/boost/boost/fusion/support/tag_of_fwd.hpp
diff --git a/third_party/boost/boost/fusion/support/tag_of_fwd.hpp b/third_party/boost/boost/fusion/support/tag_of_fwd.hpp
new file mode 100644
index 0000000000000000000000000000000000000000..e6c883d5dc7c076c2ba94c6baf6d5424309cf0a8
--- /dev/null
+++ b/third_party/boost/boost/fusion/support/tag_of_fwd.hpp
@@ -0,0 +1,20 @@
+/*=============================================================================
+    Copyright (c) 2001-2006 Joel de Guzman
+    Copyright (c) 2005-2006 Dan Marsden
+
+    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)
+==============================================================================*/
+#if !defined(BOOST_FUSION_TAG_OF_FWD_31122005_1445)
+#define BOOST_FUSION_TAG_OF_FWD_31122005_1445
+
+namespace boost { namespace fusion
+{
+    namespace traits
+    {
+        template<typename T, typename Active = void>
+        struct tag_of;
+    }
+}}
+
+#endif