Implement a way to add browser capabilities:

* There is currently no way to define specific browser capabilities since our SystemTest driver override the `option` key [Ref](https://github.com/rails/rails/blob/a07d0680787ced3c04b362fa7a238c918211ac70/actionpack/lib/action_dispatch/system_testing/driver.rb#L35)
  This option key is used internally by selenium to add custom capabilities on the browser.

  Depending on the Browser, some option are allowed to be passed inside a hash, the driver takes care of setting whatever you passed on the driver option. An example [here](https://github.com/rails/rails/blob/a07d0680787ced3c04b362fa7a238c918211ac70/actionpack/lib/action_dispatch/system_testing/driver.rb#L35) where you are allowed to pass args such as `--no-sandbox` etc
  However this behavior was only meant for backward compatibility and as you can see it's deprecated.
  The non-deprecated behavior is to create a `<Driver>::Option` object containing all the capabilities we want. This is what we [currently do](https://github.com/rails/rails/blob/a07d0680787ced3c04b362fa7a238c918211ac70/actionpack/lib/action_dispatch/system_testing/browser.rb#L34-L36) when chrome or firefox are in headless mode.

  This PR allows to pass a block when calling `driven_by`, the block will be pased a `<Driver>::Option` instance. You can modify this object the way you want by adding any capabilities. The option object will be then passed to selenium.

  ```ruby
    driven_by :selenium, using: :chrome do |driver_option|
      driver_option.add_argument('--no-sandbox')
      driver_option.add_emulation(device: 'iphone 4')
    end
  ```

1 files changed, 1 insertions, 0 deletions

diff --git a/Gemfile.lock b/Gemfile.lock
index 1f02b9c4c7..62be590ffb 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -568,6 +568,7 @@ DEPENDENCIES
   rubocop (>= 0.47)
   sass-rails
   sdoc (~> 1.0)
+  selenium-webdriver (~> 3.5.1)
   sequel
   sidekiq
   sneakers