Print error when removed webview attribute is used (backport: 3-0-x) (#14274)

* chore: print error when removed webview attribute is used

* docs: document removed webview features

lib/browser/api/web-contents.js

@@ -264,6 +264,12 @@ WebContents.prototype.getZoomFactor = function (callback) {
   })
 }
 
+// TODO(zcbenz): Remove the stub in 4.0.
+WebContents.prototype.setSize = function () {
+  console.error('The WebContents.setSize method has been removed, see',
+                'https://github.com/electron/electron/issues/14120 for more.')
+}
+
 // Add JavaScript wrappers for WebContents class.
 WebContents.prototype._init = function () {
   // The navigation controller.