tools: implement blob close

Implement blob close call.

Change-Id: If7c845e1e3b542e6f0253136eb8b6fd40bc96f3d
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/tools/blob_interface.hpp b/tools/blob_interface.hpp
index 7e22849..b79121b 100644
--- a/tools/blob_interface.hpp
+++ b/tools/blob_interface.hpp
@@ -47,6 +47,13 @@
     virtual std::uint16_t
         openBlob(const std::string& id,
                  blobs::FirmwareBlobHandler::UpdateFlags handlerFlags) = 0;
+
+    /**
+     * Attempt to close the open session.
+     *
+     * @param[in] session - the session to close.
+     */
+    virtual void closeBlob(std::uint16_t session) = 0;
 };
 
 } // namespace host_tool