RELEASE_ASSERT if last resort fallback font cannot be loaded.

Source/platform/fonts/FontFallbackList.cpp

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  *
  * 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 126 matching lines @@
 
     for (unsigned fontIndex = 0; ; ++fontIndex) {
         const FontData* fontData = fontDataAt(fontDescription, fontIndex);
         if (!fontData) {
             // All fonts are custom fonts and are loading. Return the first FontData.
             fontData = fontDataAt(fontDescription, 0);
             if (fontData)
                 return fontData->fontDataForCharacter(space);
 
             SimpleFontData* lastResortFallback = FontCache::fontCache()->getLastResortFallbackFont(fontDescription).get();
-            ASSERT(lastResortFallback);
+            RELEASE_ASSERT(lastResortFallback);
             return lastResortFallback;
         }
 
         if (fontData->isSegmented() && !toSegmentedFontData(fontData)->containsCharacter(space))
             continue;
 
         const SimpleFontData* fontDataForSpace = fontData->fontDataForCharacter(space);
         ASSERT(fontDataForSpace);
 
         // When a custom font is loading, we should use the correct fallback font to layout the text.
@@ skipping 80 matching lines @@
     RefPtr<FontData> result = getFontData(fontDescription, m_familyIndex);
     if (result) {
         m_fontList.append(result);
         if (result->isLoadingFallback())
             m_hasLoadingFallback = true;
     }
     return result.get();
 }
 
 } // namespace blink