Add a constructor to TextIterator taking two Positions as iteration range.

Source/core/editing/TextIterator.h

Index: Source/core/editing/TextIterator.h
diff --git a/Source/core/editing/TextIterator.h b/Source/core/editing/TextIterator.h
index 9d73d8add4d2efc3cdb64e76554a2bc2982e141d..73832fcaa9f1f8f269fc0a8c59d7a5ff2689f4a9 100644
--- a/Source/core/editing/TextIterator.h
+++ b/Source/core/editing/TextIterator.h
@@ -87,6 +87,8 @@ private:
 class TextIterator {
 public:
     explicit TextIterator(const Range*, TextIteratorBehaviorFlags = TextIteratorDefaultBehavior);
+    // [start, end] indicates the document range that the iteration should take place within (both ends inclusive).
+    TextIterator(const Position& start, const Position& end, TextIteratorBehaviorFlags = TextIteratorDefaultBehavior);
     ~TextIterator();
 
     bool atEnd() const { return !m_positionNode || m_shouldStop; }
@@ -128,6 +130,8 @@ private:
         HandledChildren
     };
 
+    void initialize(const Position& start, const Position& end);
+
     int startOffset() const { return m_positionStartOffset; }
     const String& string() const { return m_text; }
     void exitNode();