Implement "replacement" text encoding.

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 741314b091a1698b05369c9ef4761e4f730e60a5..328657c7e2a9399948f5289c0de895830471e258 100644
--- a/Source/modules/encoding/TextEncoder.cpp
+++ b/Source/modules/encoding/TextEncoder.cpp
@@ -55,12 +55,12 @@ PassRefPtrWillBeRawPtr<TextEncoder> TextEncoder::create(const String& utfLabel,
         return nullptr;
     }
 
-    return adoptRefWillBeNoop(new TextEncoder(encoding.name()));
+    return adoptRefWillBeNoop(new TextEncoder(encodingLabel, name));
 }
 
-TextEncoder::TextEncoder(const String& encoding)
-    : m_encoding(encoding)
-    , m_codec(newTextCodec(m_encoding))
+TextEncoder::TextEncoder(const String& label, const String& name)
+    : m_encoding(name)
+    , m_codec(newTextCodec(label))
 {
 }
 
@@ -70,7 +70,7 @@ TextEncoder::~TextEncoder()
 
 String TextEncoder::encoding() const
 {
-    String name = String(m_encoding.name()).lower();
+    String name = m_encoding.lower();
     ASSERT(name == "utf-8" || name == "utf-16le" || name == "utf-16be");
     return name;
 }