XMLHttpRequest::overrideMimeType should throw InvalidStateError

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 30c501640c68d1f1d7c453ae08f7ca615b3f6e22..82177442b8837cf04c73b695ae6c8633dca5b886 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -1033,12 +1033,14 @@ void XMLHttpRequest::handleRequestError(ExceptionCode exceptionCode, const Atomi
     dispatchProgressEvent(EventTypeNames::loadend, receivedLength, expectedLength);
 }
 
-void XMLHttpRequest::overrideMimeType(const AtomicString& override)
+void XMLHttpRequest::overrideMimeType(const AtomicString& mimeType, ExceptionState& exceptionState)
 {
-    // FIXME: This method must throw an InvalidStateError exception when the
-    // XHR is in the LOADING or DONE state. http://crbug.com/402375
+    if (m_state == LOADING || m_state == DONE) {
+        exceptionState.throwDOMException(InvalidStateError, "MimeType cannot be overridden when the state is LOADING or DONE.");
+        return;
+    }
 
-    m_mimeTypeOverride = override;
+    m_mimeTypeOverride = mimeType;
 }
 
 void XMLHttpRequest::setRequestHeader(const AtomicString& name, const AtomicString& value, ExceptionState& exceptionState)