Don't turn middleclicks into click events.

LayoutTests/fast/events/script-tests/mouse-click-events.js

 description("This tests what mouse events we send.");
 
 var div = document.createElement("div");
 div.style.width = "100px";
 div.style.height = "100px";
 div.style.backgroundColor = "blue";
 
 var eventLog = "";
 
 function appendEventLog() {
@@ skipping 11 matching lines @@
 div.addEventListener("click", appendEventLog, false);
 div.addEventListener("dblclick", appendEventLog, false);
 div.addEventListener("mousedown", appendEventLog, false);
 div.addEventListener("mouseup", appendEventLog, false);
 document.body.insertBefore(div, document.body.firstChild);
 
 if (window.eventSender)
     eventSender.mouseMoveTo(10, 10);
 
 function sendEvents(button) {
+    if (button < 0 || button > 2) {
+        testFailed("eventSender only supports button 0 (left), 1 (middle) and 2 (right).");
+        return;
+    }
     if (!window.eventSender) {
         debug("This test requires DumpRenderTree.  Click on the blue rect with different mouse buttons to log.")
         return;
     }
     eventSender.mouseDown(button);
     eventSender.mouseUp(button);
     eventSender.mouseDown(button);
     eventSender.mouseUp(button);
     // could test dragging here too
 }
 
 function testEvents(description, button, expectedString) {
     debug(description);
     sendEvents(button);
     shouldBeEqualToString("eventLog", expectedString);
     clearEventLog();
 }
 
 if (window.eventSender) {
     testEvents("Left Mouse Button", 0, "mousedown(0) mouseup(0) click(0) mousedown(0) mouseup(0) click(0) dblclick(0) ");
-    testEvents("Middle Mouse Button", 1, "mousedown(1) mouseup(1) click(1) mousedown(1) mouseup(1) click(1) dblclick(1) ");
+    testEvents("Middle Mouse Button", 1, "mousedown(1) mouseup(1) mousedown(1) mouseup(1) ");
     testEvents("Right Mouse Button", 2, "mousedown(2) mouseup(2) mousedown(2) mouseup(2) ");
-    testEvents("4th Mouse Button", 3, "mousedown(1) mouseup(1) click(1) mousedown(1) mouseup(1) click(1) dblclick(1) ");
 }