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

Source/platform/fonts/shaping/HarfBuzzShaper.cpp

 /*
  * Copyright (c) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 BlackBerry Limited. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 427 matching lines @@
             numWordEnds++;
     }
 
     if (numWordEnds)
         m_padPerWordBreak = m_padding / numWordEnds;
     else
         m_padPerWordBreak = 0;
 }
 
 
-void HarfBuzzShaper::setDrawRange(unsigned from, unsigned to)
+void HarfBuzzShaper::setDrawRange(int from, int to)
 {
+    ASSERT_WITH_SECURITY_IMPLICATION(from >= 0);
     ASSERT_WITH_SECURITY_IMPLICATION(to <= m_run.length());
     m_fromIndex = from;
     m_toIndex = to;
 }
 
 void HarfBuzzShaper::setFontFeatures()
 {
     const FontDescription& description = m_font->fontDescription();
     if (description.orientation() == Vertical) {
         static hb_feature_t vert = { HarfBuzzFace::vertTag, 1, 0, static_cast<unsigned>(-1) };
@@ skipping 695 matching lines @@
             point.x() + fromX, point.x() + toX,
             point.y(), height);
     }
 
     return Font::pixelSnappedSelectionRect(
         point.x() + toX, point.x() + fromX,
         point.y(), height);
 }
 
 } // namespace blink