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..d54a59bda86a030c94b04326dd606cf383169916 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -977,6 +977,12 @@ WebInputEventResult EventHandler::handleMousePressEvent(const PlatformMouseEvent
 {
     TRACE_EVENT0("blink", "EventHandler::handleMousePressEvent");
 
+    // 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)
+        return WebInputEventResult::HandledSuppressed;
+
     RefPtrWillBeRawPtr<FrameView> protector(m_frame->view());
 
     UserGestureIndicator gestureIndicator(DefinitelyProcessingUserGesture);
@@ -1305,6 +1311,12 @@ WebInputEventResult EventHandler::handleMouseReleaseEvent(const PlatformMouseEve
 {
     TRACE_EVENT0("blink", "EventHandler::handleMouseReleaseEvent");
 
+    // 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)
+        return WebInputEventResult::HandledSuppressed;
+
     RefPtrWillBeRawPtr<FrameView> protector(m_frame->view());
 
     m_frame->selection().setCaretBlinkingSuspended(false);