Implements the interfaces that FakeBluetoothChooser overrides. The
mojom::FakeBluetoothChooser overrides are implemented by running
|event_handler_| with the appropriate arguments. The BluetoothChooser
overrides do nothing at the moment, since the base class is only meant
to update the chooser user interface.

This change also begins to partially convert a Bluetooth chooser test to test
the interface and deletes the temporary tests that were created to test this
API.

This change reverts commit 42624492cd5e80855f1dd3a5a8146b258def2c2a, which
reverted the original change. The original change caused the
new-scan-device-added.html test to fail because of a Mojo validation error
resulting from not updating the
third_party/.../external/wpt/resources/chromium/fake_bluetooth_chooser.mojom.js
file needed by the test.

Bug: 719827, 719826, 824704, 826787
Change-Id: I5e5cce7e809b4d71216c2d074a417ea822d5e527
Reviewed-on: https://chromium-review.googlesource.com/985195
Commit-Queue: Ovidio Henriquez <odejesush@chromium.org>
Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546729}