Work on heap and space initialization to support image loading

Change-Id: Icab25efa4dee17e4b6c6e97e38f63f5ab8a8a005
diff --git a/src/file_linux.h b/src/file_linux.h
index 7e36ada..3d381d5 100644
--- a/src/file_linux.h
+++ b/src/file_linux.h
@@ -22,6 +22,10 @@
   virtual off_t Length();
   virtual off_t Position();
 
+  virtual int Fd() {
+    return fd_;
+  }
+
  private:
   static const int kClosedFd = -1;