Add a path for content/ to open and control a Bluetooth chooser dialog.

This obsoletes several histogram values, and some of the corner-case error states won't be well tested until I add the ability for layout tests to manage dialog states.

2nd of 3 patches:
1. Add errors and prepare tests. (https://codereview.chromium.org/1293593003/)
2. Wire up the chooser on the Chrome side. (This patch)
3. Update the test assertions and remove now-unused errors. (https://codereview.chromium.org/1284143006/)

BUG=500989, 517237

Review URL: https://codereview.chromium.org/1286063002

Cr-Commit-Position: refs/heads/master@{#345541}
12 files changed