GitLab

Adds BluetoothAdapter::Observer callbacks to Adapter implementation
for tracking changes in Adapter state including:
  AdapterDiscoverableChanged
  AdapterPoweredChanged
  AdapterPresentChanged

Adds adapter page to display details about the current state of the adapter.
Adds ObjectFieldSet interface component for displaying properties of a JavaScript object.

Screenshot: https://goo.gl/photos/dCbsULiydMbiAtiJ9

BUG=651282
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2567983007
Cr-Commit-Position: refs/heads/master@{#443065}