add the 'webpreferences' attribute to webviews

lib/browser/guest-view-manager.js

@@ -184,6 +184,31 @@ const attachGuest = function (embedder, elementInstanceId, guestInstanceId, para
     disableBlinkFeatures: params.disableblinkfeatures
   }
 
+  // parse the 'webpreferences' attribute string, if set
+  // this uses the same parsing rules as window.open uses for its features
+  if (typeof params.webpreferences === 'string') {
+    // split the attribute's value by ','
+    let webpreferencesTokens = params.webpreferences.split(/,\s*/)
+    for (i = 0, len = webpreferencesTokens.length; i < len; i++) {
+      // expected form is either a name by itself (true boolean flag)
+      // or a key/value, in the form of 'name=value'
+      // split the tokens by '='
+      let pref = webpreferencesTokens[i]
+      let prefTokens = pref.split(/\s*=/)
+      name = prefTokens[0]
+      value = prefTokens[1]
+      if (!name) continue
+
+      // interpret the value as a boolean, if possible 
+      value = (value === 'yes' || value === '1') ? true : (value === 'no' || value === '0') ? false : value
+      if (value === undefined) {
+        // no value was specified, default it to true
+        value = true
+      }
+      webPreferences[name] = value
+    }
+  }
+
   if (params.preload) {
     webPreferences.preloadURL = params.preload
   }