Elements whose contents start with an astral Unicode symbol disappear when CSS `::first-letter` is …

Source/platform/text/TextBreakIterator.h

Index: Source/platform/text/TextBreakIterator.h
diff --git a/Source/platform/text/TextBreakIterator.h b/Source/platform/text/TextBreakIterator.h
index 72187c6c3cc7f1c2deba1dfcfb85bbf31b531645..b595ab5da98030f0c0af295d3bd272044eae37af 100644
--- a/Source/platform/text/TextBreakIterator.h
+++ b/Source/platform/text/TextBreakIterator.h
@@ -30,6 +30,15 @@
 
 namespace blink {
 
+struct ClusterData {
+    ClusterData(unsigned numGraphemes, unsigned numCharacters)
+        : graphemes(numGraphemes)
+        , characters(numCharacters)
+    { }
+    unsigned graphemes;
+    unsigned characters;
+};
+
 typedef icu::BreakIterator TextBreakIterator;
 
 // Note: The returned iterator is good only until you get another iterator, with the exception of acquireLineBreakIterator.
@@ -255,6 +264,8 @@ private:
 // of a non-combining character and following combining characters is
 // counted as 1 grapheme cluster.
 PLATFORM_EXPORT unsigned numGraphemeClusters(const String&);
+// Counts the number of graphemes and characters.
+PLATFORM_EXPORT ClusterData countCharactersAndGraphemesInCluster(const UChar* normalizedBuffer, unsigned normalizedBufferLength, uint16_t startIndex, uint16_t endIndex);
 
 }