Bug 99020, need to clear the value of a textbox when we change its type to

'file.' r=heikki, sr=jst.

content/html/content/src/nsHTMLInputElement.cpp

@@ -1293,6 +1293,10 @@ nsHTMLInputElement::StringToAttribute(nsIAtom* aAttribute,
     nsAutoString valueStr(aValue);
     while (nsnull != table->tag) { 
       if (valueStr.EqualsIgnoreCase(table->tag)) {
+        // If the type is being changed to file, set the element value
+        // to the empty string. This is for security.
+        if (table->value == NS_FORM_INPUT_FILE)
+          SetValue(NS_LITERAL_STRING(""));
         aResult.SetIntValue(table->value, eHTMLUnit_Enumerated);
         mType = table->value;  // set the type of this input
         return NS_CONTENT_ATTR_HAS_VALUE;