XMLHttpRequest should clear the response encoding when it clears responseText.

Source/core/xml/XMLHttpRequest.cpp

Index: Source/core/xml/XMLHttpRequest.cpp
diff --git a/Source/core/xml/XMLHttpRequest.cpp b/Source/core/xml/XMLHttpRequest.cpp
index 01089b1c9ea6213daa6eebc8e317fc3c5b82fa69..282afdab5166c04df88916d33ba7781716363cc0 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -831,6 +831,7 @@ void XMLHttpRequest::clearResponse()
 void XMLHttpRequest::clearResponseBuffers()
 {
     m_responseText.clear();
+    m_responseEncoding = String();
     m_createdDocument = false;
     m_responseDocument = 0;
     m_responseBlob = 0;
@@ -1082,6 +1083,7 @@ void XMLHttpRequest::didFinishLoading(unsigned long identifier, double)
     m_loader = 0;
 
     changeState(DONE);
+    m_responseEncoding = String();
     m_decoder = 0;
 
     if (hadLoader)