Prevent direct use of "replacement" text encoding.

Source/wtf/text/TextEncoding.cpp

Index: Source/wtf/text/TextEncoding.cpp
diff --git a/Source/wtf/text/TextEncoding.cpp b/Source/wtf/text/TextEncoding.cpp
index 9adff579120c04ae646a1759407d88bc778569a0..f232e57b2acc6613c5ad807f290a396013ef1504 100644
--- a/Source/wtf/text/TextEncoding.cpp
+++ b/Source/wtf/text/TextEncoding.cpp
@@ -47,12 +47,18 @@ TextEncoding::TextEncoding(const char* name)
     : m_name(atomicCanonicalTextEncodingName(name))
     , m_backslashAsCurrencySymbol(backslashAsCurrencySymbol())
 {
+    // Aliases are valid, but not "replacement" itself.
+    if (m_name && isReplacementEncoding(name))
+        m_name = 0;
 }
 
 TextEncoding::TextEncoding(const String& name)
     : m_name(atomicCanonicalTextEncodingName(name))
     , m_backslashAsCurrencySymbol(backslashAsCurrencySymbol())
 {
+    // Aliases are valid, but not "replacement" itself.
+    if (m_name && isReplacementEncoding(name))
+        m_name = 0;
 }
 
 String TextEncoding::decode(const char* data, size_t length, bool stopOnError, bool& sawError) const