Gracefully support Navigator Gamepad methods in a detached state.

If the frame and window of a Navigator has been detached (closed), the
Navigator Gamepad methods must still continue to be available. Arrange
for that to happen by allowing the Gamepad Navigator supplement to
be creatable without a frame.

R=
BUG=355783

Review URL: https://codereview.chromium.org/256593010

git-svn-id: svn://svn.chromium.org/blink/trunk@172920 bbb929c8-8fbe-4397-9dbb-9b2b20218538
13 files changed