Expose desktopCapturer in sandbox mode.

lib/sandboxed_renderer/api/exports/electron.js

@@ -32,5 +32,15 @@ Object.defineProperties(exports, {
     get: function () {
       return require('../../../common/api/is-promise')
     }
+  },
+  desktopCapturer: {
+    get: function () {
+      return require('../../../renderer/api/desktop-capturer')
+    }
+  },
+  nativeImage: {
+    get: function () {
+      return require('../../../common/api/native-image')
+    }
   }
 })