Provide user friendly messages for OTS parsing of fonts

Source/platform/fonts/opentype/OpenTypeSanitizer.cpp

Index: Source/platform/fonts/opentype/OpenTypeSanitizer.cpp
diff --git a/Source/platform/fonts/opentype/OpenTypeSanitizer.cpp b/Source/platform/fonts/opentype/OpenTypeSanitizer.cpp
index c5e71ae45976e36add0d0c78f017cdfcaa0c23f9..77a62f5057cf8aa6d9120be8d34abed8bc5f54a8 100644
--- a/Source/platform/fonts/opentype/OpenTypeSanitizer.cpp
+++ b/Source/platform/fonts/opentype/OpenTypeSanitizer.cpp
@@ -77,9 +77,14 @@ PassRefPtr<SharedBuffer> OpenTypeSanitizer::sanitize()
     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);