window interface: add close method

Add a close method, that when called does whatever is appropriate for
the given implementation.

Note: There are a few methods that don't map nicely, and therefore it
makes sense to add a close() to this interface.

Change-Id: If001446b2248715ea76147ea35a99a729ba5a404
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/test/window_mapper_mock.hpp b/test/window_mapper_mock.hpp
index 4d401c4..c8a75c6 100644
--- a/test/window_mapper_mock.hpp
+++ b/test/window_mapper_mock.hpp
@@ -16,6 +16,7 @@
   public:
     virtual ~HardwareInterfaceMock() = default;
 
+    MOCK_METHOD0(close, ());
     MOCK_METHOD2(mapWindow,
                  std::pair<std::uint32_t, std::uint32_t>(std::uint32_t,
                                                          std::uint32_t));