OTS: Adds more layout common table supports....

include/ots-memory-stream.h

Index: include/ots-memory-stream.h
===================================================================
--- include/ots-memory-stream.h	(revision 50)
+++ include/ots-memory-stream.h	(working copy)
@@ -18,7 +18,7 @@
       : ptr_(ptr), length_(length), off_(0) {
   }
 
-  bool WriteRaw(const void *data, size_t length) {
+  virtual bool WriteRaw(const void *data, size_t length) {
     if ((off_ + length > length_) ||
         (length > std::numeric_limits<size_t>::max() - off_)) {
       return false;
@@ -28,14 +28,14 @@
     return true;
   }
 
-  bool Seek(off_t position) {
+  virtual bool Seek(off_t position) {
     if (position < 0) return false;
     if (static_cast<size_t>(position) > length_) return false;
     off_ = position;
     return true;
   }
 
-  off_t Tell() const {
+  virtual off_t Tell() const {
     return off_;
   }