static: add temporary filename for staging update

Add the filename planned to use for stage the update.  This location was
chosen because a rename operation can happen locally within the folder,
such that it's an inode change and not a data copy.

Change-Id: I2868e8409325f0ee4bcd71f653a2e81355a5cefe
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/static_handler.hpp b/static_handler.hpp
index 65076d7..edb3df5 100644
--- a/static_handler.hpp
+++ b/static_handler.hpp
@@ -16,7 +16,8 @@
     /**
      * Create a StaticLayoutHandler.
      */
-    StaticLayoutHandler() = default;
+    explicit StaticLayoutHandler(const std::string& temporaryName) :
+        stagedFilename(temporaryName){};
 
     bool open(const std::string& path) override;
 
@@ -25,6 +26,9 @@
 
   private:
     std::string path;
+
+    /** The file to use for staging the bytes. */
+    std::string stagedFilename;
 };
 
 } // namespace blobs