Added Base64 support in TextEncoder and TextDecoder.

Source/wtf/text/TextEncoding.h

Index: Source/wtf/text/TextEncoding.h
diff --git a/Source/wtf/text/TextEncoding.h b/Source/wtf/text/TextEncoding.h
index 1e4aa7b3f683f8135a38cd9c8103a78086464b0b..937b31d23576415ae4975d087975197529faba9b 100644
--- a/Source/wtf/text/TextEncoding.h
+++ b/Source/wtf/text/TextEncoding.h
@@ -72,6 +72,7 @@ inline bool operator==(const TextEncoding& a, const TextEncoding& b) { return a.
 inline bool operator!=(const TextEncoding& a, const TextEncoding& b) { return a.name() != b.name(); }
 
 WTF_EXPORT const TextEncoding& ASCIIEncoding();
+WTF_EXPORT const TextEncoding& Base64Encoding();
 WTF_EXPORT const TextEncoding& Latin1Encoding();
 WTF_EXPORT const TextEncoding& UTF16BigEndianEncoding();
 WTF_EXPORT const TextEncoding& UTF16LittleEndianEncoding();
@@ -83,6 +84,7 @@ WTF_EXPORT const TextEncoding& WindowsLatin1Encoding();
 } // namespace WTF
 
 using WTF::ASCIIEncoding;
+using WTF::Base64Encoding;
 using WTF::Latin1Encoding;
 using WTF::UTF16BigEndianEncoding;
 using WTF::UTF16LittleEndianEncoding;