Handle missing glyphs when adjusting spacing in SimpleShaper

Source/platform/fonts/shaping/SimpleShaper.cpp

Index: Source/platform/fonts/shaping/SimpleShaper.cpp
diff --git a/Source/platform/fonts/shaping/SimpleShaper.cpp b/Source/platform/fonts/shaping/SimpleShaper.cpp
index 24be19b9ee933caae0e3af3b62499483fc314198..1206d19a1ae991145a88e7e26e3e55e3fe36dfcc 100644
--- a/Source/platform/fonts/shaping/SimpleShaper.cpp
+++ b/Source/platform/fonts/shaping/SimpleShaper.cpp
@@ -190,10 +190,12 @@ unsigned SimpleShaper::advanceInternal(TextIterator& textIterator, GlyphBuffer*
         // 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.

         }
@@ -207,7 +209,7 @@ unsigned SimpleShaper::advanceInternal(TextIterator& textIterator, GlyphBuffer*
             cacheFallbackFont(fontData, primaryFont);
         }
 
-        if (hasExtraSpacing)
+        if (hasExtraSpacing && !spaceUsedAsZeroWidthSpace)
             width = adjustSpacing(width, charData, *fontData, glyphBuffer);
 
         if (m_bounds)