Work on heap and space initialization to support image loading

Change-Id: Icab25efa4dee17e4b6c6e97e38f63f5ab8a8a005
diff --git a/src/file.h b/src/file.h
index 680872e..3353602 100644
--- a/src/file.h
+++ b/src/file.h
@@ -33,6 +33,8 @@
   // Returns a negative value if position cannot be determined.
   virtual off_t Position() = 0;
 
+  virtual int Fd() = 0;
+
   const char* name() const { return name_; }
 
  protected: