[Mac] Enter should trigger the buttons in the new avatar bubble.

Only space seems to work by default.

BUG=415823

Review URL: https://codereview.chromium.org/644023002

Cr-Commit-Position: refs/heads/master@{#299157}

chrome/browser/ui/cocoa/profiles/profile_chooser_controller.mm

@@ -36,6 +36,7 @@
 #include "chrome/browser/ui/chrome_style.h"
 #import "chrome/browser/ui/cocoa/info_bubble_view.h"
 #import "chrome/browser/ui/cocoa/info_bubble_window.h"
+#import "chrome/browser/ui/cocoa/key_equivalent_constants.h"
 #import "chrome/browser/ui/cocoa/profiles/user_manager_mac.h"
 #include "chrome/browser/ui/singleton_tabs.h"
 #include "chrome/browser/ui/user_manager.h"
@@ -2106,6 +2107,7 @@ class ActiveProfileObserverBridge : public AvatarMenuObserver,
   [button setBordered:NO];
   [button setTarget:self];
   [button setAction:action];
+  [button setKeyEquivalent:kKeyEquivalentReturn];
 
   return button.autorelease();
 }