Revert "[sanitize] Remove now-unused set_object() machinery"

This reverts commit bbdb6edb3e.

src/hb-machinery.hh

@@ -259,11 +259,34 @@ struct hb_sanitize_context_t :
 
   inline void set_max_ops (int max_ops_) { max_ops = max_ops_; }
 
-  inline void start_processing (void)
+  template <typename T>
+  inline void set_object (const T& obj)
+  {
+    reset_object ();
+
+    const char *obj_start = (const char *) &obj;
+    const char *obj_end = (const char *) &obj + obj.get_size ();
+    assert (obj_start <= obj_end); /* Must not overflow. */
+
+    if (unlikely (obj_end < this->start || this->end < obj_start))
+      this->start = this->end = nullptr;
+    else
+    {
+      this->start = MAX (this->start, obj_start);
+      this->end   = MIN (this->end  , obj_end  );
+    }
+  }
+
+  inline void reset_object (void)
   {
     this->start = this->blob->data;
     this->end = this->start + this->blob->length;
     assert (this->start <= this->end); /* Must not overflow. */
+  }
+
+  inline void start_processing (void)
+  {
+    reset_object ();
     this->max_ops = MAX ((unsigned int) (this->end - this->start) * HB_SANITIZE_MAX_OPS_FACTOR,
 			 (unsigned) HB_SANITIZE_MAX_OPS_MIN);
     this->edit_count = 0;