Revert of TextRun::length() should return an unsigned

Source/core/rendering/svg/SVGTextMetricsBuilder.cpp

Index: Source/core/rendering/svg/SVGTextMetricsBuilder.cpp
diff --git a/Source/core/rendering/svg/SVGTextMetricsBuilder.cpp b/Source/core/rendering/svg/SVGTextMetricsBuilder.cpp
index 711aa32c23ef41d161c03960ff220718ffdb09e4..5f3cbf0ea0b6f1c7d3ea9a705291674a8be1d448 100644
--- a/Source/core/rendering/svg/SVGTextMetricsBuilder.cpp
+++ b/Source/core/rendering/svg/SVGTextMetricsBuilder.cpp
@@ -18,6 +18,7 @@
  */
 
 #include "config.h"
+
 #include "core/rendering/svg/SVGTextMetricsBuilder.h"
 
 #include "core/rendering/svg/RenderSVGInline.h"
@@ -42,7 +43,7 @@
     ~SVGTextMetricsCalculator();
 
     SVGTextMetrics computeMetricsForCharacter(unsigned textPosition);
-    unsigned textLength() const { return m_run.charactersLength(); }
+    unsigned textLength() const { return static_cast<unsigned>(m_run.charactersLength()); }
 
     bool characterStartsSurrogatePair(unsigned textPosition) const
     {