[Line Layout API] Add textStartOffset to LineLayoutText

Source/core/layout/api/LineLayoutText.h

Index: Source/core/layout/api/LineLayoutText.h
diff --git a/Source/core/layout/api/LineLayoutText.h b/Source/core/layout/api/LineLayoutText.h
index bc884cb22e8090c6d433eb4d4d74d11b6b4f24bb..ba5efd0284d81d6c1e5b7439bf7d2e69ce966c41 100644
--- a/Source/core/layout/api/LineLayoutText.h
+++ b/Source/core/layout/api/LineLayoutText.h
@@ -122,6 +122,11 @@ public:
         return toText()->selectionStartEnd(spos, epos);
     }
 
+    unsigned textStartOffset() const
+    {
+        return toText()->textStartOffset();
+    }
+
 private:
     LayoutText* toText() { return toLayoutText(layoutObject()); }
     const LayoutText* toText() const { return toLayoutText(layoutObject()); }