Provide user friendly messages for OTS parsing of fonts

Source/platform/fonts/opentype/OpenTypeSanitizer.cpp

 /*
  * Copyright (C) 2009 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 59 matching lines @@
     // However, it can be slightly bigger than the original one due to
     // name table replacement and/or padding for glyf table.
     //
     // With WOFF fonts, however, we'll be decompressing, so the result can be
     // much larger than the original.
 
     ots::ExpandingMemoryStream output(m_buffer->size(), maxWebFontSize);
     double start = currentTime();
     BlinkOTSContext otsContext;
 
-    if (!otsContext.Process(&output, reinterpret_cast<const uint8_t*>(m_buffer->data()), m_buffer->size()))
+    if (!otsContext.Process(&output, reinterpret_cast<const uint8_t*>(m_buffer->data()), m_buffer->size())) {
+        setParsingError(true);
+        setErrorString(otsContext.getErrorString());
         return nullptr;
+    }
 
+    setParsingError(false);
+    setErrorString(otsContext.getErrorString());
     const size_t transcodeLen = output.Tell();
     recordDecodeSpeedHistogram(m_buffer, currentTime() - start, transcodeLen);
     return SharedBuffer::create(static_cast<unsigned char*>(output.get()), transcodeLen);
 }
 
 bool OpenTypeSanitizer::supportsFormat(const String& format)
 {
     return equalIgnoringCase(format, "woff") || equalIgnoringCase(format, "woff2");
 }
 
 } // namespace blink