Don't turn middleclicks into click events.

Source/core/page/EventHandler.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 1637 matching lines @@
         return true;
 
     bool swallowMouseUpEvent = !dispatchMouseEvent(eventNames().mouseupEvent, mev.targetNode(), true, m_clickCount, mouseEvent, false);
 
     bool contextMenuEvent = mouseEvent.button() == RightButton;
 #if OS(DARWIN)
     // FIXME: The Mac port achieves the same behavior by checking whether the context menu is currently open in WebPage::mouseEvent(). Consider merging the implementations.
     if (mouseEvent.button() == LeftButton && mouseEvent.modifiers() & PlatformEvent::CtrlKey)
         contextMenuEvent = true;
 #endif
-
-    bool swallowClickEvent = m_clickCount > 0 && !contextMenuEvent && mouseIsReleasedOnPressedElement(mev.targetNode(), m_clickNode.get()) && !dispatchMouseEvent(eventNames().clickEvent, mev.targetNode(), true, m_clickCount, mouseEvent, true);
+    bool isMiddleOnLink = false;
+    if (mouseEvent.button() == MiddleButton) {
+        // Middle clicks on links result in the links being opened in a background tab. It's important to not also
+        // dispatch a click event since that might make the link execute twice.
+        WebCore::Node* node = mev.targetNode();

[abarth-chromium, 2013/09/06 05:01:25]

"WebCore::" <-- no need for this namespace.  We're already in the WebCore
namespace.

+        while (node && !node->isLink())
+            node = node->parentNode();

[abarth-chromium, 2013/09/06 05:01:25]

Hum...  This crawling around the DOM doesn't seem like it can be right.

+        if (node)
+            isMiddleOnLink = true;
+    }
+    bool swallowClickEvent = false;
+    if (m_clickCount > 0 && !contextMenuEvent && !isMiddleOnLink && mouseIsReleasedOnPressedElement(mev.targetNode(), m_clickNode.get())) {
+        // Turn the Mouse Button Released event into a click event since all requirements are fulfilled.
+        swallowClickEvent = !dispatchMouseEvent(eventNames().clickEvent, mev.targetNode(), true, m_clickCount, mouseEvent, true);
+    }
 
     if (m_resizeLayer) {
         m_resizeLayer->setInResizeMode(false);
         m_resizeLayer = 0;
     }
 
     bool swallowMouseReleaseEvent = false;
     if (!swallowMouseUpEvent)
         swallowMouseReleaseEvent = handleMouseReleaseEvent(mev);
 
@@ skipping 2174 matching lines @@
 unsigned EventHandler::accessKeyModifiers()
 {
 #if OS(DARWIN)
     return PlatformEvent::CtrlKey | PlatformEvent::AltKey;
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace WebCore