Make UTF-8 encoding of unpaired surrogates match Encoding standard

Source/wtf/text/TextCodecUTF8.cpp

Index: Source/wtf/text/TextCodecUTF8.cpp
diff --git a/Source/wtf/text/TextCodecUTF8.cpp b/Source/wtf/text/TextCodecUTF8.cpp
index ce595b34619709488d0e20aa31b955afaeeb08f3..f26f3031c9620dfdbacef299834cab27e0dd7ab5 100644
--- a/Source/wtf/text/TextCodecUTF8.cpp
+++ b/Source/wtf/text/TextCodecUTF8.cpp
@@ -436,6 +436,8 @@ CString TextCodecUTF8::encodeCommon(const CharType* characters, size_t length)
     while (i < length) {
         UChar32 character;
         U16_NEXT(characters, i, length, character);
+        if (0xD800 <= character && character <= 0xDFFF)
+            character = 0xFFFD;

[jungshik at Google, 2013/08/30 00:39:27]

For a future code archaeologist, could you add a comment to the effect that
"U16_NEXT" will set |character| to a surrogate code point (U+D800 .. U+DFFF)
when coming across an unmatched surrogate code point" and we have to convert it
to a replacement character. 

[jsbell, 2013/08/30 00:43:56]

Will do. I'll also use WTF::Unicode::replacementCharacter which I discovered
after uploading this.

         U8_APPEND_UNSAFE(bytes.data(), bytesWritten, character);
     }