Added Base64 support in TextEncoder and TextDecoder.

LayoutTests/fast/encoding/api/encoding-names.html

Index: LayoutTests/fast/encoding/api/encoding-names.html
diff --git a/LayoutTests/fast/encoding/api/encoding-names.html b/LayoutTests/fast/encoding/api/encoding-names.html
index 6a8a3efbaa934d6b08045846b147f9d1b5125cf9..be12dd3c94261a63c67c8e59951fd7326def240b 100644
--- a/LayoutTests/fast/encoding/api/encoding-names.html
+++ b/LayoutTests/fast/encoding/api/encoding-names.html
@@ -11,7 +11,8 @@ var encodings = [
     { label: 'utf-16le', encoding: 'utf-16le' },
     { label: 'utf-16be', encoding: 'utf-16be' },
     { label: 'ascii', encoding: 'windows-1252' },
-    { label: 'iso-8859-1', encoding: 'windows-1252' }
+    { label: 'iso-8859-1', encoding: 'windows-1252' },
+    { label: 'base64', encoding: 'base64' }
 ];
 
 // encoding-labels.html tests the full set of names/labels; this test just