Add support for shaping a substring to HarfBuzzShaper

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

Index: third_party/WebKit/Source/platform/fonts/shaping/RunSegmenter.h
diff --git a/third_party/WebKit/Source/platform/fonts/shaping/RunSegmenter.h b/third_party/WebKit/Source/platform/fonts/shaping/RunSegmenter.h
index 19b1b6bf3f2d653620e61dd3709bc6a5d7106d52..186e7ec45f7a73718b23052c955a5922ea6fbd22 100644
--- a/third_party/WebKit/Source/platform/fonts/shaping/RunSegmenter.h
+++ b/third_party/WebKit/Source/platform/fonts/shaping/RunSegmenter.h
@@ -41,6 +41,11 @@ class PLATFORM_EXPORT RunSegmenter {
 
   bool consume(RunSegmenterRange*);
 
+  static RunSegmenterRange nullRange() {
+    return {0, 0, USCRIPT_INVALID_CODE, OrientationIterator::OrientationInvalid,
+            FontFallbackPriority::Invalid};
+  }
+
  private:
   void consumeOrientationIteratorPastLastSplit();
   void consumeScriptIteratorPastLastSplit();