Handle fonts with missing ZWS glyph in simple text path

Source/platform/fonts/WidthIterator.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 170 matching lines @@
         && !m_run.spacingDisabled();
 
     const SimpleFontData* primaryFont = m_font->primaryFont();
     const SimpleFontData* lastFontData = primaryFont;
     bool normalizeSpace = m_run.normalizeSpace();
 
     CharacterData charData;
     while (textIterator.consume(charData.character, charData.clusterLength)) {
         charData.characterOffset = textIterator.currentCharacter();
 
-        const GlyphData glyphData = glyphDataForCharacter(charData, normalizeSpace);
+        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;
+        if (!glyphData.glyph && Character::treatAsZeroWidthSpaceInComplexScript(charData.character)) {
+            charData.character = space;
+            glyphData = glyphDataForCharacter(charData);
+            width = 0;
+        } else {
+            width = characterWidth(charData.character, glyphData);
+        }
+
         Glyph glyph = glyphData.glyph;
         const SimpleFontData* fontData = glyphData.fontData;
         ASSERT(fontData);
 
-        // Now that we have a glyph and font data, get its width.
-        float width = characterWidth(charData.character, glyphData);
-
         if (m_fallbackFonts && lastFontData != fontData && width) {
             lastFontData = fontData;
             cacheFallbackFont(fontData, primaryFont);
         }
 
         if (hasExtraSpacing)
             width = adjustSpacing(width, charData, *fontData, glyphBuffer);
 
         if (m_accountForGlyphBounds)
             updateGlyphBounds(glyphData, width, !charData.characterOffset);
@@ skipping 39 matching lines @@
     float initialWidth = m_runWidthSoFar;
 
     if (!advance(m_currentCharacter + 1))
         return false;
 
     width = m_runWidthSoFar - initialWidth;
     return true;
 }
 
 } // namespace blink