Use IDL argument default values in modules/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 a669e0272d11dec6c3a1ad3e3f6a4def86744287..284bd49008694b1eac4901fc4f8a8e0eae022f80 100644
--- a/Source/modules/encoding/TextEncoder.cpp
+++ b/Source/modules/encoding/TextEncoder.cpp
@@ -41,17 +41,15 @@ namespace WebCore {
 
 TextEncoder* TextEncoder::create(const String& utfLabel, ExceptionState& exceptionState)
 {
-    const String& encodingLabel = utfLabel.isNull() ? String("utf-8") : utfLabel;
-
-    WTF::TextEncoding encoding(encodingLabel);
+    WTF::TextEncoding encoding(utfLabel);
     if (!encoding.isValid()) {
-        exceptionState.throwTypeError("The encoding label provided ('" + encodingLabel + "') is invalid.");
+        exceptionState.throwTypeError("The encoding label provided ('" + utfLabel + "') is invalid.");
         return 0;
     }
 
     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'.");
+        exceptionState.throwTypeError("The encoding provided ('" + utfLabel + "') is not one of 'utf-8', 'utf-16', or 'utf-16be'.");
         return 0;
     }
 
@@ -84,12 +82,10 @@ PassRefPtr<Uint8Array> TextEncoder::encode(const String& input, const Dictionary
     // handle split surrogates here.
 
     CString result;
-    if (!input.isNull()) {
-        if (input.is8Bit())
-            result = m_codec->encode(input.characters8(), input.length(), WTF::QuestionMarksForUnencodables);
-        else
-            result = m_codec->encode(input.characters16(), input.length(), WTF::QuestionMarksForUnencodables);
-    }
+    if (input.is8Bit())
+        result = m_codec->encode(input.characters8(), input.length(), WTF::QuestionMarksForUnencodables);
+    else
+        result = m_codec->encode(input.characters16(), input.length(), WTF::QuestionMarksForUnencodables);
 
     const char* buffer = result.data();
     const unsigned char* unsignedBuffer = reinterpret_cast<const unsigned char*>(buffer);