Handle missing glyphs when adjusting spacing in SimpleShaper

Source/platform/fonts/shaping/SimpleShaper.cpp

 /*
  * Copyright (C) 2003, 2006, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Holger Hans Peter Freyther
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 172 matching lines @@
 
     CharacterData charData;
     while (textIterator.consume(charData.character, charData.clusterLength)) {
         charData.characterOffset = textIterator.currentCharacter();
 
         GlyphData glyphData = glyphDataForCharacter(charData, normalizeSpace);
 
         // Some fonts do not have a glyph for zero-width-space,
         // in that case use the space character and override the width.
         float width;
+        bool spaceUsedAsZeroWidthSpace = false;
         if (!glyphData.glyph && Character::treatAsZeroWidthSpaceInComplexScript(charData.character)) {
             charData.character = space;
             glyphData = glyphDataForCharacter(charData);
             width = 0;
+            spaceUsedAsZeroWidthSpace = true;
         } else {
             width = characterWidth(charData.character, glyphData);

[pdr., 2014/10/14 00:28:36]

Would it make sense to add
ASSERT(!fontData.isZeroWidthSpaceGlyph(fontData.glyphForCharacter(charData.character)))
here?

[eae, 2014/10/14 00:30:36]

Not really, we only go down the fallback-path above if the character is both a
zero-width-space glyph _and_ the font is missing said glyph.

         }
 
         Glyph glyph = glyphData.glyph;
         const SimpleFontData* fontData = glyphData.fontData;
         ASSERT(fontData);
 
         if (m_fallbackFonts && lastFontData != fontData && width) {
             lastFontData = fontData;
             cacheFallbackFont(fontData, primaryFont);
         }
 
-        if (hasExtraSpacing)
+        if (hasExtraSpacing && !spaceUsedAsZeroWidthSpace)
             width = adjustSpacing(width, charData, *fontData, glyphBuffer);
 
         if (m_bounds)
             updateGlyphBounds(glyphData, width, !charData.characterOffset);
 
         if (m_forTextEmphasis && !Character::canReceiveTextEmphasis(charData.character))
             glyph = 0;
 
         // Advance past the character we just dealt with.
         textIterator.advance(charData.clusterLength);
@@ skipping 33 matching lines @@
     float initialWidth = m_runWidthSoFar;
 
     if (!advance(m_currentCharacter + 1))
         return false;
 
     width = m_runWidthSoFar - initialWidth;
     return true;
 }
 
 } // namespace blink