Added Base64 support in TextEncoder and TextDecoder.

Source/modules/encoding/TextEncoder.cpp

Index: Source/modules/encoding/TextEncoder.cpp
diff --git a/Source/modules/encoding/TextEncoder.cpp b/Source/modules/encoding/TextEncoder.cpp
index 1a26de62da91172943bc0777b555554af6340709..5047b11e91b93f9b9644e91f32b6d4ad5dc68d41 100644
--- a/Source/modules/encoding/TextEncoder.cpp
+++ b/Source/modules/encoding/TextEncoder.cpp
@@ -50,8 +50,8 @@ PassRefPtr<TextEncoder> TextEncoder::create(const String& utfLabel, ExceptionSta
     }
 
     String name(encoding.name());
-    if (name != "UTF-8" && name != "UTF-16LE" && name != "UTF-16BE") {
-        exceptionState.throwTypeError("The encoding provided ('" + encodingLabel + "') is not one of 'utf-8', 'utf-16', or 'utf-16be'.");
+    if (name != "UTF-8" && name != "UTF-16LE" && name != "UTF-16BE" && name != "Base64") {
+        exceptionState.throwTypeError("The encoding provided ('" + encodingLabel + "') is not one of 'utf-8', 'utf-16', 'utf-16be', or 'base64'.");
         return 0;
     }
 
@@ -71,7 +71,7 @@ TextEncoder::~TextEncoder()
 String TextEncoder::encoding() const
 {
     String name = String(m_encoding.name()).lower();
-    ASSERT(name == "utf-8" || name == "utf-16le" || name == "utf-16be");
+    ASSERT(name == "utf-8" || name == "utf-16le" || name == "utf-16be" || name == "base64");
     return name;
 }