Shape across HarfBuzz runs

Source/platform/fonts/harfbuzz/HarfBuzzShaper.cpp

Index: Source/platform/fonts/harfbuzz/HarfBuzzShaper.cpp
diff --git a/Source/platform/fonts/harfbuzz/HarfBuzzShaper.cpp b/Source/platform/fonts/harfbuzz/HarfBuzzShaper.cpp
index 10abf5082fc7759397880cb6558c57d7499d309f..2ab156bca6d0e2bce142b9b51d23395077e9d6e9 100644
--- a/Source/platform/fonts/harfbuzz/HarfBuzzShaper.cpp
+++ b/Source/platform/fonts/harfbuzz/HarfBuzzShaper.cpp
@@ -636,7 +636,6 @@ static inline bool collectCandidateRuns(const UChar* normalizedBuffer,
         const SimpleFontData* currentFontData = nextFontData;
         UScriptCode currentScript = nextScript;
 
-        UChar32 lastCharacter = character;
         for (iterator.advance(clusterLength); iterator.consume(character, clusterLength); iterator.advance(clusterLength)) {
             if (Character::treatAsZeroWidthSpace(character))
                 continue;
@@ -651,12 +650,9 @@ static inline bool collectCandidateRuns(const UChar* normalizedBuffer,
             nextScript = uscript_getScript(character, &errorCode);
             if (U_FAILURE(errorCode))
                 return false;
-            if (lastCharacter == zeroWidthJoiner)
-                currentFontData = nextFontData;
             if ((nextFontData != currentFontData) || ((currentScript != nextScript) && (nextScript != USCRIPT_INHERITED) && (!uscript_hasScript(character, currentScript))))
                 break;
             currentCharacterPosition = iterator.characters();
-            lastCharacter = character;
         }
 
         CandidateRun run = { character, startIndexOfCurrentRun, iterator.currentCharacter(), currentFontData, currentScript };
@@ -861,11 +857,13 @@ bool HarfBuzzShaper::shapeHarfBuzzRuns()
         hb_buffer_add_utf16(harfBuzzBuffer.get(), &preContext, 1, 1, 0);
 
         if (fontDescription.variant() == FontVariantSmallCaps && u_islower(m_normalizedBuffer[currentRun->startIndex()])) {
-            String upperText = String(m_normalizedBuffer.get() + currentRun->startIndex(), currentRun->numCharacters()).upper();
+            String upperText = String(m_normalizedBuffer.get(), m_normalizedBufferLength).upper();
             ASSERT(!upperText.is8Bit()); // m_normalizedBuffer is 16 bit, therefore upperText is 16 bit, even after we call makeUpper().
-            hb_buffer_add_utf16(harfBuzzBuffer.get(), toUint16(upperText.characters16()), currentRun->numCharacters(), 0, currentRun->numCharacters());
+            hb_buffer_add_utf16(harfBuzzBuffer.get(), toUint16(upperText.characters16()), currentRun->startIndex(), currentRun->startIndex(), 0);
+            hb_buffer_add_utf16(harfBuzzBuffer.get(), toUint16(upperText.characters16() + currentRun->startIndex()), m_normalizedBufferLength - currentRun->startIndex(), 0, currentRun->numCharacters());
         } else {
-            hb_buffer_add_utf16(harfBuzzBuffer.get(), toUint16(m_normalizedBuffer.get() + currentRun->startIndex()), currentRun->numCharacters(), 0, currentRun->numCharacters());
+            hb_buffer_add_utf16(harfBuzzBuffer.get(), toUint16(m_normalizedBuffer.get()), currentRun->startIndex(), currentRun->startIndex(), 0);
+            hb_buffer_add_utf16(harfBuzzBuffer.get(), toUint16(m_normalizedBuffer.get() + currentRun->startIndex()), m_normalizedBufferLength - currentRun->startIndex(), 0, currentRun->numCharacters());
         }
 
         if (fontDescription.orientation() == Vertical)