RenderTextHarfBuzz: Allow mid-glyph cursors in multi-grapheme clusters

base/i18n/break_iterator.h

Index: base/i18n/break_iterator.h
diff --git a/base/i18n/break_iterator.h b/base/i18n/break_iterator.h
index b34c6770d10fa7badd5c1a50ec290e9c8cf53491..8120d4729a22491dc9cdc1421d6aa1d4d1d5912d 100644
--- a/base/i18n/break_iterator.h
+++ b/base/i18n/break_iterator.h
@@ -106,6 +106,10 @@ class BASE_I18N_EXPORT BreakIterator {
   bool IsEndOfWord(size_t position) const;
   bool IsStartOfWord(size_t position) const;
 
+  // Under BREAK_CHARACTER mode, returns whether |position| is a Unicode
+  // grapheme boundary.
+  bool IsGraphemeBoundary(size_t position) const;
+
   // Returns the string between prev() and pos().
   // Advance() must have been called successfully at least once for pos() to
   // have advanced to somewhere useful.