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

Source/core/rendering/svg/SVGTextMetrics.cpp

Index: Source/core/rendering/svg/SVGTextMetrics.cpp
diff --git a/Source/core/rendering/svg/SVGTextMetrics.cpp b/Source/core/rendering/svg/SVGTextMetrics.cpp
index 687c93deb5f4c1851d41985aa48d1fe1408e8eb6..26dbc4c75075827367b4c475970eae2c5c7d077a 100644
--- a/Source/core/rendering/svg/SVGTextMetrics.cpp
+++ b/Source/core/rendering/svg/SVGTextMetrics.cpp
@@ -50,11 +50,14 @@
     ASSERT(scalingFactor);
 
     const Font& scaledFont = textRenderer->scaledFont();
-    m_length = 0;
+    int length = 0;
 
     // Calculate width/height using the scaled font, divide this result by the scalingFactor afterwards.
-    m_width = scaledFont.width(run, m_length, m_glyph) / scalingFactor;
+    m_width = scaledFont.width(run, length, m_glyph) / scalingFactor;
     m_height = scaledFont.fontMetrics().floatHeight() / scalingFactor;
+
+    ASSERT(length >= 0);
+    m_length = static_cast<unsigned>(length);
 }
 
 TextRun SVGTextMetrics::constructTextRun(RenderSVGInlineText* text, unsigned position, unsigned length)