Enable pinch to zoom inside iframe - Ionic 2 AngularJS 2
I think it is not possible to do in a IFrame as that will be a security flaw.what you are basically doing is trying to access a webpage from your mobile hybrid app (Ionic App in your case).it must not allow you to run javascript on that webpage, workaround for it will be by disabling web security on that browser or in your case webview (not sure how to do that in mobile but that is manual browser customization so will not work in your scenario).
more explanation on this post SecurityError: Blocked a frame with origin from accessing a cross-origin frame