Google Inc. has only Official google search app in windows phone store. EcoMerc has released unofficial Gmail App for windows phone in April, 2014. This app is one of the best app to access Gmail on windows phone and this is as close as you will experience in official gmail app.
Finally as whatsapp updated to its new version with bug fixes and new features, Whatsapp locker has provided us a feature to lock whatsapp on windows phone. Whatsapp locker will ask for a password first and after putting password it will directly open whatsapp.