Patch hb_set implementation back to pre 1.6.1 implementation again

Perf bisects indicate that the hb_set changes may be the reason for seing
performance regressions in issues 781794 and 782220. The previous CL for
patching the set implementation back [1] shows that this makes the performance
graphs recover. In [2] we reduced the number of calls to
HasSpaceInLigaturesOrKerning in an attempt to see whether this can address the
performance regressions. However, the graphs in [3] show that even after
Chromium revision 522394 (which is the revision for [3]) the graphs are not
recovering.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/804374
[2] https://chromium-review.googlesource.com/c/chromium/src/+/809106
[3] https://chromeperf.appspot.com/group_report?bug_id=781794

Bug: 782220
Change-Id: Ib4708dbba70a36d1f7659ab00dfe8222e8623d8b
Tbr: eae, kojii, behdad
Reviewed-on: https://chromium-review.googlesource.com/816795Reviewed-by: Dominik Röttsches <drott@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522757}

third_party/harfbuzz-ng/README.chromium

@@ -19,4 +19,7 @@ for removed or added files and update our build recipes in BUILD.gn and
 harfbuzz.gyp accordingly, update the NEWS file from HarfBuzz' release notes, and
 bump the version numbers in README.chromium.
 
-Locally patch hb-private.hh to silence unusued variable warnings in MSVC.
+Locally patch hb-private.hh to silence unusued variable warnings in MSVC.
\ No newline at end of file
+
+Locally patching hb_set implementation back to the pre 1.6.1 implemention as we
+observe a set of timeToFirst*Paint performance regressions in issue 781794.

third_party/harfbuzz-ng/src/hb-set.cc

@@ -45,8 +45,7 @@ hb_set_create (void)
   if (!(set = hb_object_create<hb_set_t> ()))
     return hb_set_get_empty ();
 
-  set->page_map.init();
-  set->pages.init();
+  set->clear ();
 
   return set;
 }
@@ -96,8 +95,7 @@ hb_set_destroy (hb_set_t *set)
 {
   if (!hb_object_destroy (set)) return;
 
-  set->page_map.finish();
-  set->pages.finish();
+  set->fini ();
 
   free (set);
 }
@@ -375,15 +373,14 @@ hb_set_symmetric_difference (hb_set_t       *set,
  * hb_set_invert:
  * @set: a set.
  *
- *
+ * 
  *
  * Since: 0.9.10
- *
- * Deprecated: 1.6.1
  **/
 void
 hb_set_invert (hb_set_t *set)
 {
+  set->invert ();
 }
 
 /**