Make Document.inputEncoding an explicit alias of Document.characterSet

Source/platform/network/FormDataBuilder.cpp

Index: Source/platform/network/FormDataBuilder.cpp
diff --git a/Source/platform/network/FormDataBuilder.cpp b/Source/platform/network/FormDataBuilder.cpp
index 0ca310783249c0700cc82adb922f41c93b815b6d..196ca0082359a3950b0bf511c60ba1e86476d72d 100644
--- a/Source/platform/network/FormDataBuilder.cpp
+++ b/Source/platform/network/FormDataBuilder.cpp
@@ -74,7 +74,7 @@ static void appendQuotedString(Vector<char>& buffer, const CString& string)
     }
 }
 
-WTF::TextEncoding FormDataBuilder::encodingFromAcceptCharset(const String& acceptCharset, const String& inputEncoding, const String& defaultCharset)
+WTF::TextEncoding FormDataBuilder::encodingFromAcceptCharset(const String& acceptCharset, const String& charset, const String& defaultCharset)
 {
     String normalizedAcceptCharset = acceptCharset;
     normalizedAcceptCharset.replace(',', ' ');
@@ -90,14 +90,14 @@ WTF::TextEncoding FormDataBuilder::encodingFromAcceptCharset(const String& accep
             return encoding;
     }
 
-    if (inputEncoding.isEmpty()) {
+    if (charset.isEmpty()) {
         if (defaultCharset.isEmpty())
             return WTF::UTF8Encoding();
 
         return defaultCharset;
     }
 
-    return inputEncoding;
+    return charset;
 }
 
 Vector<char> FormDataBuilder::generateUniqueBoundaryString()