Suppress mouseup/down when button is NoButton

Chrome sends the mousedown/up in some cases
when the 4th/5th button is pressed/released
without actually sending that button value as
we don't have yet the plumbing needed for that.

BUG=574959

Review URL: https://codereview.chromium.org/1824733006

Cr-Commit-Position: refs/heads/master@{#383812}

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

@@ -978,6 +978,12 @@ 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);
@@ -1300,6 +1306,12 @@ 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);