Initialize GamepadService in BrowserThreadsStarted

The gamepad service needs a service manager connector in order
to connect to the device service. This CL adds a startup step in
BrowserThreadsStarted to provide the service manager connector.
This connector should only be used from the polling thread.

BUG=801717

Change-Id: Ia56479fb9e300f0b52b682bd7a905e9271efa7a9
Reviewed-on: https://chromium-review.googlesource.com/c/1362102
Reviewed-by: Ovidio Henriquez <odejesush@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614472}
5 files changed