Right now PermissionTestRule starts an EmbeddedTestServer directly.

This makes it impossible to use alongside any other test rule that starts a test server directly (eg see the refactor I had to do here[1] of NotificationTestRule to extract an EmbeddedTestServerRule in order to use both a NotificationTestRule and a PermissionTestRule here[2])

PermissionTestRule would be more composable if it depended on an EmbeddedTestServerRule that could be passed in, or didn't depend on one at all if that's possible.

[1] Refactor of NotificationTestRule: https://chromium-review.googlesource.com/c/chromium/src/+/1142148

[2] which enabled: https://chromium-review.googlesource.com/c/chromium/src/+/1145309