[subset] add an inprogress accelerator to plan.

This allows subset code to cache information into the accelerator during preprocess subset. Previously the accelerator was created at the end of subsetting.

src/hb-subset-plan.cc

@@ -926,6 +926,17 @@ hb_subset_plan_create_or_fail (hb_face_t	 *face,
     hb_subset_plan_destroy (plan);
     return nullptr;
   }
+
+
+  if (plan->attach_accelerator_data)
+  {
+    plan->inprogress_accelerator =
+      hb_subset_accelerator_t::create (*plan->codepoint_to_glyph,
+                                       *plan->unicodes,
+				       plan->has_seac);
+  }
+
+
   return plan;
 }
 

src/hb-subset-plan.hh

@@ -96,6 +96,9 @@ struct hb_subset_plan_t
     hb_hashmap_destroy (name_table_overrides);
 #endif
 
+    if (inprogress_accelerator)
+      hb_subset_accelerator_t::destroy ((void*) inprogress_accelerator);
+
     if (user_axes_location)
     {
       hb_object_destroy (user_axes_location);
@@ -209,6 +212,7 @@ struct hb_subset_plan_t
 #endif
 
   const hb_subset_accelerator_t* accelerator;
+  hb_subset_accelerator_t* inprogress_accelerator;
 
  public:
 

src/hb-subset.cc

@@ -499,13 +499,14 @@ _subset_table (hb_subset_plan_t *plan,
   }
 }
 
-static void _attach_accelerator_data (const hb_subset_plan_t* plan,
+static void _attach_accelerator_data (hb_subset_plan_t* plan,
                                       hb_face_t* face /* IN/OUT */)
 {
-  hb_subset_accelerator_t* accel =
-      hb_subset_accelerator_t::create (*plan->codepoint_to_glyph,
-                                       *plan->unicodes,
-				       plan->has_seac);
+  if (!plan->inprogress_accelerator) return;
+
+  // Transfer the accelerator from the plan to us.
+  hb_subset_accelerator_t* accel = plan->inprogress_accelerator;
+  plan->inprogress_accelerator = nullptr;
 
   if (accel->in_error ())
   {