[repacker] Expose on internal method in the repacker that allows the caller to pass in/out a graph.

Will be used in testing so we can compare graphs instead of packed result.

src/graph/graph.hh

diff --git a/src/graph/graph.hh b/src/graph/graph.hh
index 5f23414..0d3dae2 100644
--- a/src/graph/graph.hh
+++ b/src/graph/graph.hh
@@ -196,7 +196,8 @@
       : parents_invalid (true),
         distance_invalid (true),
         positions_invalid (true),
-        successful (true)
+        successful (true),
+        buffers ()
   {
     num_roots_for_space_.push (1);
     bool removed_nil = false;
@@ -228,6 +229,8 @@
   ~graph_t ()
   {
     vertices_.fini ();
+    for (char* b : buffers)
+      hb_free (b);
   }
 
   bool in_error () const
@@ -255,6 +258,11 @@
     return vertices_[i].obj;
   }
 
+  void add_buffer (char* buffer)
+  {
+    buffers.push (buffer);
+  }
+
   /*
    * Adds a 16 bit link from parent_id to child_id
    */
@@ -1127,6 +1135,7 @@
   bool positions_invalid;
   bool successful;
   hb_vector_t<unsigned> num_roots_for_space_;
+  hb_vector_t<char*> buffers;
 };
 
 }

src/graph/gsubgpos-context.cc

diff --git a/src/graph/gsubgpos-context.cc b/src/graph/gsubgpos-context.cc
index e0ff6ff..b204442 100644
--- a/src/graph/gsubgpos-context.cc
+++ b/src/graph/gsubgpos-context.cc
@@ -33,8 +33,7 @@
     : table_tag (table_tag_),
       graph (graph_),
       lookup_list_index (0),
-      lookups (),
-      buffers ()
+      lookups ()
 {
   if (table_tag_ != HB_OT_TAG_GPOS
       &&  table_tag_ != HB_OT_TAG_GSUB)
@@ -53,7 +52,7 @@
   if (!buffer)
     return -1;
 
-  buffers.push (buffer);
+  add_buffer (buffer);
 
   return graph.new_node (buffer, buffer + size);
 }

src/graph/gsubgpos-context.hh

diff --git a/src/graph/gsubgpos-context.hh b/src/graph/gsubgpos-context.hh
index 49b2419..9fe9662 100644
--- a/src/graph/gsubgpos-context.hh
+++ b/src/graph/gsubgpos-context.hh
@@ -40,22 +40,16 @@
   graph_t& graph;
   unsigned lookup_list_index;
   hb_hashmap_t<unsigned, graph::Lookup*> lookups;
-  hb_vector_t<char*> buffers;
+
 
   HB_INTERNAL gsubgpos_graph_context_t (hb_tag_t table_tag_,
                                         graph_t& graph_);
 
-  ~gsubgpos_graph_context_t ()
-  {
-    for (char* b : buffers)
-      hb_free (b);
-  }
-
   HB_INTERNAL unsigned create_node (unsigned size);
 
   void add_buffer (char* buffer)
   {
-    buffers.push (buffer);
+    graph.add_buffer (buffer);
   }
 
  private: