Make Document.inputEncoding an explicit alias of Document.characterSet

Source/core/loader/FormSubmission.cpp

Index: Source/core/loader/FormSubmission.cpp
diff --git a/Source/core/loader/FormSubmission.cpp b/Source/core/loader/FormSubmission.cpp
index 55542318b453b14dc38a58c68840a4309675267b..c6d966abb6721acb665f72d297b70921ee422cec 100644
--- a/Source/core/loader/FormSubmission.cpp
+++ b/Source/core/loader/FormSubmission.cpp
@@ -208,7 +208,7 @@ PassRefPtrWillBeRawPtr<FormSubmission> FormSubmission::create(HTMLFormElement* f
             isMultiPartForm = false;
         }
     }
-    WTF::TextEncoding dataEncoding = isMailtoForm ? UTF8Encoding() : FormDataBuilder::encodingFromAcceptCharset(copiedAttributes.acceptCharset(), document.inputEncoding(), document.defaultCharset());
+    WTF::TextEncoding dataEncoding = isMailtoForm ? UTF8Encoding() : FormDataBuilder::encodingFromAcceptCharset(copiedAttributes.acceptCharset(), document.charset(), document.defaultCharset());
     RefPtrWillBeRawPtr<DOMFormData> domFormData = DOMFormData::create(dataEncoding.encodingForFormSubmission());
 
     bool containsPasswordData = false;