Suppress mouseup/down when button is NoButton

third_party/WebKit/Source/core/input/EventHandler.cpp

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index 8581d36a79c4af94e669f85882d3a333dabe3376..7df48290df4c2e2cd810e2ac6a1e701a363e3611 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -1375,12 +1375,19 @@ WebInputEventResult EventHandler::handleMouseReleaseEvent(const PlatformMouseEve
         if (Node* clickTargetNode = mev.innerNode()->commonAncestor(
             *m_clickNode, parentForClickEvent)) {
 
-            // Dispatch mouseup directly w/o calling updateMouseEventTargetNode
-            // because the mouseup dispatch above has already updated it
-            // correctly. Moreover, clickTargetNode is different from
-            // mev.innerNode at drag-release.
-            clickEventResult = toWebInputEventResult(clickTargetNode->dispatchMouseEvent(mev.event(),
-                EventTypeNames::click, m_clickCount));
+            // For 4th/5th button in the mouse since Chrome does not yet send
+            // button value to Blink but in some cases it does send the event.
+            // This check is needed to suppress such an event (crbug.com/574959)
+            if (mouseEvent.button() == NoButton) {
+                clickEventResult = WebInputEventResult::HandledSystem;

[mustaq, 2016/03/23 19:13:26]

I think we should make those buttons completely ineffective, not even changing
focus etc above. I suggest adding the "bailout code" earlier, near the entry
point to EventHandler, and keep the "deeper" code intact. I mean at both
handleMousePressEvent(PlatformMouseEvent&) and
handleMouseReleaseEvent(PlatformMouseEvent&).

+            } else {
+                // Dispatch mouseup directly w/o calling updateMouseEventTargetNode
+                // because the mouseup dispatch above has already updated it
+                // correctly. Moreover, clickTargetNode is different from
+                // mev.innerNode at drag-release.
+                clickEventResult = toWebInputEventResult(clickTargetNode->dispatchMouseEvent(mev.event(),
+                    EventTypeNames::click, m_clickCount));
+            }
         }
     }
 
@@ -1680,6 +1687,12 @@ WebInputEventResult EventHandler::updatePointerTargetAndDispatchEvents(const Ato
         || mouseEventType == EventTypeNames::mousemove
         || mouseEventType == EventTypeNames::mouseup);
 
+    // For 4th/5th button in the mouse since Chrome does not yet send
+    // button value to Blink but in some cases it does send the event.
+    // This check is needed to suppress such an event (crbug.com/574959)
+    if (mouseEventType != EventTypeNames::mousemove && mouseEvent.button() == NoButton)
+        return WebInputEventResult::HandledSystem;
+
     updateMouseEventTargetNode(targetNode, mouseEvent);
     if (!m_nodeUnderMouse)
         return WebInputEventResult::NotHandled;