Only check the keycode for key events.

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

Index: chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm
diff --git a/chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm b/chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm
index e008d3d79c9b0287ac557ccaeb34dd3c7a3eda80..44ce222b0e321a8aa72d68ee55aeef3e595e8af4 100644
--- a/chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm
+++ b/chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm
@@ -846,7 +846,9 @@ bool OmniboxViewMac::OnDoCommandBySelector(SEL cmd) {
   // 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);