Add 8bit Content-Transfer-Encoding support for reading MHTML files

Source/core/platform/network/MIMEHeader.cpp

Index: Source/core/platform/network/MIMEHeader.cpp
diff --git a/Source/core/platform/network/MIMEHeader.cpp b/Source/core/platform/network/MIMEHeader.cpp
index 2c40a9bca7bcc46b535916aa2934b3170fa2920c..7e56eeac47f7b720030f27136b4a2c6d191d99db 100644
--- a/Source/core/platform/network/MIMEHeader.cpp
+++ b/Source/core/platform/network/MIMEHeader.cpp
@@ -120,6 +120,8 @@ MIMEHeader::Encoding MIMEHeader::parseContentTransferEncoding(const String& text
         return Base64;
     if (encoding == "quoted-printable")
         return QuotedPrintable;
+    if (encoding == "8bit")
+        return EightBit;
     if (encoding == "7bit")
         return SevenBit;
     if (encoding == "binary")