Replace responseType mismatch handling code in XMLHttpRequest::responseJSONSource() with ASSERT

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 ced9f078707ad8d5b350cce6c2c61cc896150ef5..645c48a8bb15103b967623c7babbd700875311c1 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -224,12 +224,10 @@ ScriptString XMLHttpRequest::responseText(ExceptionState& es)
     return m_responseText;
 }
 
-ScriptString XMLHttpRequest::responseJSONSource(ExceptionState& es)
+ScriptString XMLHttpRequest::responseJSONSource()
 {
-    if (m_responseTypeCode != ResponseTypeJSON) {
-        es.throwDOMException(InvalidStateError);
-        return ScriptString();
-    }
+    ASSERT(m_responseTypeCode == ResponseTypeJSON);
+
     if (m_error || m_state != DONE)
         return ScriptString();
     return m_responseText;