Ignore Return and Cmd+Return in the omnibox if no text has been entered.

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 05dd79f60aa29b9f2c517163933ed491ae3fa921..8c1457c4f6ddaa452cf7d430f62956f660778080 100644
--- a/chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm
+++ b/chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm
@@ -817,6 +817,11 @@ bool OmniboxViewMac::OnDoCommandBySelector(SEL cmd) {
      (cmd == @selector(noop:) &&
       ([event type] == NSKeyDown || [event type] == NSKeyUp) &&
       [event keyCode] == kVK_Return)) {
+    // If the user hasn't entered any text in keyword search mode, we need to
+    // return early in order to avoid cancelling the search.
+    if (GetTextLength() == 0)
+      return true;
+
     WindowOpenDisposition disposition =
         ui::WindowOpenDispositionFromNSEvent(event);
     model()->AcceptInput(disposition, false);