Replace most uses of is_inert with is_immutable
diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index 5a8152e..1a5547b 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -217,7 +217,7 @@
 void
 hb_buffer_t::reset (void)
 {
-  if (unlikely (hb_object_is_inert (this)))
+  if (unlikely (hb_object_is_immutable (this)))
     return;
 
   hb_unicode_funcs_destroy (unicode);
@@ -232,7 +232,7 @@
 void
 hb_buffer_t::clear (void)
 {
-  if (unlikely (hb_object_is_inert (this)))
+  if (unlikely (hb_object_is_immutable (this)))
     return;
 
   hb_segment_properties_t default_props = HB_SEGMENT_PROPERTIES_DEFAULT;
@@ -289,7 +289,7 @@
 void
 hb_buffer_t::remove_output (void)
 {
-  if (unlikely (hb_object_is_inert (this)))
+  if (unlikely (hb_object_is_immutable (this)))
     return;
 
   have_output = false;
@@ -302,7 +302,7 @@
 void
 hb_buffer_t::clear_output (void)
 {
-  if (unlikely (hb_object_is_inert (this)))
+  if (unlikely (hb_object_is_immutable (this)))
     return;
 
   have_output = true;
@@ -315,7 +315,7 @@
 void
 hb_buffer_t::clear_positions (void)
 {
-  if (unlikely (hb_object_is_inert (this)))
+  if (unlikely (hb_object_is_immutable (this)))
     return;
 
   have_output = false;
@@ -873,7 +873,7 @@
 hb_buffer_set_unicode_funcs (hb_buffer_t        *buffer,
 			     hb_unicode_funcs_t *unicode_funcs)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   if (!unicode_funcs)
@@ -920,7 +920,7 @@
 			 hb_direction_t  direction)
 
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->props.direction = direction;
@@ -964,7 +964,7 @@
 hb_buffer_set_script (hb_buffer_t *buffer,
 		      hb_script_t  script)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->props.script = script;
@@ -1008,7 +1008,7 @@
 hb_buffer_set_language (hb_buffer_t   *buffer,
 			hb_language_t  language)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->props.language = language;
@@ -1046,7 +1046,7 @@
 hb_buffer_set_segment_properties (hb_buffer_t *buffer,
 				  const hb_segment_properties_t *props)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->props = *props;
@@ -1082,7 +1082,7 @@
 hb_buffer_set_flags (hb_buffer_t       *buffer,
 		     hb_buffer_flags_t  flags)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->flags = flags;
@@ -1118,7 +1118,7 @@
 hb_buffer_set_cluster_level (hb_buffer_t       *buffer,
 		     hb_buffer_cluster_level_t  cluster_level)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->cluster_level = cluster_level;
@@ -1157,7 +1157,7 @@
 hb_buffer_set_replacement_codepoint (hb_buffer_t    *buffer,
 				     hb_codepoint_t  replacement)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->replacement = replacement;
@@ -1197,7 +1197,7 @@
 hb_buffer_set_invisible_glyph (hb_buffer_t    *buffer,
 			       hb_codepoint_t  invisible)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   buffer->invisible = invisible;
@@ -1329,7 +1329,7 @@
 hb_buffer_set_length (hb_buffer_t  *buffer,
 		      unsigned int  length)
 {
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return length == 0;
 
   if (!buffer->ensure (length))
@@ -1535,7 +1535,7 @@
   assert (buffer->content_type == HB_BUFFER_CONTENT_TYPE_UNICODE ||
 	  (!buffer->len && buffer->content_type == HB_BUFFER_CONTENT_TYPE_INVALID));
 
-  if (unlikely (hb_object_is_inert (buffer)))
+  if (unlikely (hb_object_is_immutable (buffer)))
     return;
 
   if (text_length == -1)
diff --git a/src/hb-coretext.cc b/src/hb-coretext.cc
index 184db49..893a876 100644
--- a/src/hb-coretext.cc
+++ b/src/hb-coretext.cc
@@ -353,7 +353,7 @@
   hb_font_t *font = hb_font_create (face);
   hb_face_destroy (face);
 
-  if (unlikely (hb_object_is_inert (font)))
+  if (unlikely (hb_object_is_immutable (font)))
     return font;
 
   hb_font_set_ptem (font, coretext_font_size_to_ptem (CTFontGetSize(ct_font)));
diff --git a/src/hb-font.cc b/src/hb-font.cc
index 567cded..b24995b 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -1377,7 +1377,7 @@
 
   hb_font_t *font = _hb_font_create (parent->face);
 
-  if (unlikely (hb_object_is_inert (font)))
+  if (unlikely (hb_object_is_immutable (font)))
     return font;
 
   font->parent = hb_font_reference (parent);
diff --git a/src/hb-set.hh b/src/hb-set.hh
index 947e8d9..21a2252 100644
--- a/src/hb-set.hh
+++ b/src/hb-set.hh
@@ -225,15 +225,17 @@
     return true;
   }
 
-  inline void clear (void) {
-    if (unlikely (hb_object_is_inert (this)))
+  inline void clear (void)
+  {
+    if (unlikely (hb_object_is_immutable (this)))
       return;
     successful = true;
     population = 0;
     page_map.resize (0);
     pages.resize (0);
   }
-  inline bool is_empty (void) const {
+  inline bool is_empty (void) const
+  {
     unsigned int count = pages.len;
     for (unsigned int i = 0; i < count; i++)
       if (!pages[i].is_empty ())
diff --git a/src/hb-shape-plan.cc b/src/hb-shape-plan.cc
index 4648cc7..8d002f8 100644
--- a/src/hb-shape-plan.cc
+++ b/src/hb-shape-plan.cc
@@ -343,7 +343,7 @@
   if (unlikely (!buffer->len))
     return true;
 
-  assert (!hb_object_is_inert (buffer));
+  assert (!hb_object_is_immutable (buffer));
   assert (buffer->content_type == HB_BUFFER_CONTENT_TYPE_UNICODE);
 
   if (unlikely (hb_object_is_inert (shape_plan)))