Only check the keycode for key events.

chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.h"
 
 #include <Carbon/Carbon.h>  // kVK_Return
 
 #include "base/string_util.h"
 #include "base/sys_string_conversions.h"
@@ skipping 828 matching lines @@
     }
 
     if (model_->AcceptCurrentInstantPreview())
       return true;
   }
 
   // |-noop:| is sent when the user presses Cmd+Return. Override the no-op
   // behavior with the proper WindowOpenDisposition.
   NSEvent* event = [NSApp currentEvent];
   if (cmd == @selector(insertNewline:) ||
-     (cmd == @selector(noop:) && [event keyCode] == kVK_Return)) {
+     (cmd == @selector(noop:) &&
+      ([event type] == NSKeyDown || [event type] == NSKeyUp) &&
+      [event keyCode] == kVK_Return)) {
     WindowOpenDisposition disposition =
         event_utils::WindowOpenDispositionFromNSEvent(event);
     model_->AcceptInput(disposition, false);
     // Opening a URL in a background tab should also revert the omnibox contents
     // to their original state.  We cannot do a blanket revert in OpenURL()
     // because middle-clicks also open in a new background tab, but those should
     // not revert the omnibox text.
     RevertAll();
     return true;
   }
@@ skipping 254 matching lines @@
 
 void OmniboxViewMac::PlaceCaretAt(NSUInteger pos) {
   DCHECK(pos <= GetTextLength());
   SetSelectedRange(NSMakeRange(pos, pos));
 }
 
 bool OmniboxViewMac::IsCaretAtEnd() const {
   const NSRange selection = GetSelectedRange();
   return selection.length == 0 && selection.location == GetTextLength();
 }