use better heuristic for maxcharwidth

Source/platform/fonts/SimpleFontData.cpp

 /*
  * Copyright (C) 2005, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 183 matching lines @@
     // arbitrary but comes pretty close to the expected value in most cases.
     if (m_maxCharWidth < 1)
         m_maxCharWidth = ascent * 2;
 #elif OS(MACOSX)
     // FIXME: The current avg/max character width calculation is not ideal,
     // it should check either the OS2 table or, better yet, query FontMetrics.
     // Sadly FontMetrics provides incorrect data on Mac at the moment.
     // https://crbug.com/420901
     m_maxCharWidth = std::max(m_avgCharWidth, m_fontMetrics.floatAscent());
 #else
-    // FIXME: This seems incorrect and should probably use fMaxCharWidth as
-    // the code path above.
-    SkScalar xRange = metrics.fXMax - metrics.fXMin;
-    m_maxCharWidth = SkScalarRoundToInt(xRange * SkScalarRoundToInt(m_platformData.size()));
+    // FIXME: Skia needs to fill in fMaxCharWidth for us. [skbug.com/3087]
+    m_maxCharWidth = std::max(m_avgCharWidth, m_fontMetrics.floatAscent());

[jbroman, 2014/10/30 19:55:20]

drive-by: this seems to be the same as the previous case; should they be merged?

 #endif
 
 #if !OS(MACOSX)
     if (metrics.fAvgCharWidth) {
         m_avgCharWidth = SkScalarRoundToInt(metrics.fAvgCharWidth);
     } else {
 #endif
         m_avgCharWidth = xHeight;
 
         GlyphPage* glyphPageZero = GlyphPageTreeNode::getRootChild(this, 0)->page();
@@ skipping 266 matching lines @@
         if (glyphs[i]) {
             pageToFill->setGlyphDataForIndex(offset + i, glyphs[i], this);
             haveGlyphs = true;
         }
     }
 
     return haveGlyphs;
 }
 
 } // namespace blink