Add support for shaping a substring to HarfBuzzShaper

third_party/WebKit/Source/platform/fonts/shaping/RunSegmenter.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef RunSegmenter_h
 #define RunSegmenter_h
 
 #include "platform/fonts/FontOrientation.h"
 #include "platform/fonts/FontTraits.h"
 #include "platform/fonts/OrientationIterator.h"
@@ skipping 23 matching lines @@
     unsigned end;
     UScriptCode script;
     OrientationIterator::RenderOrientation renderOrientation;
     FontFallbackPriority fontFallbackPriority;
   };
 
   RunSegmenter(const UChar* buffer, unsigned bufferSize, FontOrientation);
 
   bool consume(RunSegmenterRange*);
 
+  static RunSegmenterRange nullRange() {
+    return {0, 0, USCRIPT_INVALID_CODE, OrientationIterator::OrientationKeep,
+            FontFallbackPriority::Text};
+  }
+
  private:
   void consumeOrientationIteratorPastLastSplit();
   void consumeScriptIteratorPastLastSplit();
   void consumeSymbolsIteratorPastLastSplit();
 
   unsigned m_bufferSize;
   RunSegmenterRange m_candidateRange;
   std::unique_ptr<ScriptRunIterator> m_scriptRunIterator;
   std::unique_ptr<OrientationIterator> m_orientationIterator;
   std::unique_ptr<SymbolsIterator> m_symbolsIterator;
   unsigned m_lastSplit;
   unsigned m_scriptRunIteratorPosition;
   unsigned m_orientationIteratorPosition;
   unsigned m_symbolsIteratorPosition;
   bool m_atEnd;
 };
 
 }  // namespace blink
 
 #endif