Add checkValidity() function HTMLFormElement and HTMLInputElement
Add checkValidity() function HTMLFormElement and HTMLInputElement

Summary: Both of these are defined in the HTML5 spec.Closes https://github.com/facebook/flow/pull/866

Reviewed By: @jeffmo

Differential Revision: D2487387

Pulled By: @gabelevi

ylu1317/flow,jamesgpearce/flow,jdelStrother/flow,mcanthony/flow-type,TiddoLangerak/flow,fletcherw/flow,claudiopro/flow,chenglou/flow,nmote/flow,chenglou/flow,facebook/flow,AgentME/flow,jgrund/flow,gabro/flow,JonathanUsername/flow,samwgoldman/flow,jamesgpearce/flow,TiddoLangerak/flow,mcanthony/flow-type,popham/flow,ForbesLindesay/flow,jamesgpearce/flow,fletcherw/flow,gabro/flow,MichaelDeBoey/flow,AgentME/flow,gabelevi/flow,jdelStrother/flow,AgentME/flow,nmote/flow,mroch/flow,popham/flow,fletcherw/flow,gabelevi/flow,claudiopro/flow,ylu1317/flow,AprilArcus/flow,claudiopro/flow,ForbesLindesay/flow,jamesgpearce/flow,jamesgpearce/flow,d14b3l/flow,JonathanUsername/flow,cesarandreu/flow,Eyyub/flow,popham/flow,OCamlPro/flow,ylu1317/flow,jeffutter/flow,mroch/flow,facebook/flow,claudiopro/flow,AprilArcus/flow,nmote/flow,jgrund/flow,popham/flow,jeffutter/flow,samwgoldman/flow,jeffmo/flow,gabro/flow,cesarandreu/flow,graue/flow,shiftcars/flow,claudiopro/flow,AprilArcus/flow,jdelStrother/flow,AgentME/flow,MichaelDeBoey/flow,facebook/flow,samwgoldman/flow,AgentME/flow,d14b3l/flow,graue/flow,jeffmo/flow,AprilArcus/flow,gabelevi/flow,fletcherw/flow,graue/flow,TiddoLangerak/flow,Eyyub/flow,jeffmo/flow,jdelStrother/flow,d14b3l/flow,popham/flow,shiftcars/flow,chenglou/flow,cesarandreu/flow,mroch/flow,jamesgpearce/flow,gabro/flow,JonathanUsername/flow,shiftcars/flow,graue/flow,gabro/flow,popham/flow,graue/flow,ylu1317/flow,jgrund/flow,ForbesLindesay/flow,jgrund/flow,mroch/flow,MichaelDeBoey/flow,popham/flow,jgrund/flow,nmote/flow,JonathanUsername/flow,mcanthony/flow-type,cesarandreu/flow,samwgoldman/flow,jeffutter/flow,gabelevi/flow,chenglou/flow,AprilArcus/flow,JonathanUsername/flow,Eyyub/flow,ForbesLindesay/flow,jamesgpearce/flow,samwgoldman/flow,fletcherw/flow,MichaelDeBoey/flow,TiddoLangerak/flow,jeffmo/flow,nmote/flow,TiddoLangerak/flow,shiftcars/flow,OCamlPro/flow,AprilArcus/flow,chenglou/flow,jdelStrother/flow,fletcherw/flow,d14b3l/flow,mroch/flow,nmote/flow,ForbesLindesay/flow,jeffutter/flow,samwgoldman/flow,shiftcars/flow,jeffmo/flow,gabelevi/flow,jeffmo/flow,ForbesLindesay/flow,Eyyub/flow,mcanthony/flow-type,ylu1317/flow,d14b3l/flow,mroch/flow,mroch/flow,chenglou/flow,MichaelDeBoey/flow,gabelevi/flow,graue/flow,facebook/flow,facebook/flow,gabro/flow,jgrund/flow,d14b3l/flow,gabelevi/flow,nmote/flow,facebook/flow,facebook/flow,shiftcars/flow,OCamlPro/flow,JonathanUsername/flow,OCamlPro/flow,JonathanUsername/flow,samwgoldman/flow,jdelStrother/flow