bluetooth: Move testing IPC from BluetoothDispatcher to BlinkTestRunner

bluetooth: Move testing IPC from BluetoothDispatcher to BlinkTestRunner

This patch removes the testing IPC from BluetoothDispatcher and
BluetoothDispatcherHost.

This patch also changes the way the mock BluetoothAdapter was set in
BluetoothDispatcherHost. Instead of receiving an IPC to set the adapter,
BluetoothDispatcherHost exposes a function to directly set the adapter.
This function is used by LayoutTestSupport to set the adapter.

Mock adapter flow before:
BlinkTestRunner -> LayoutTestSupport -> BluetoothDispatcher --IPC-->
BluetoothDispatcherHost (Mock constructed here)

After:
BlinkTestRunner --IPC--> LayoutTestMessages(Mock constructed here) ->
LayoutTestSupport -> BluetoothDispatcherHost

This is the first of two patches to remove testing from BluetoothDispatcher
and BluetoothDispatcherHost:

 [1] This patch.
 [2] http://crrev.com/1132943002

BUG=436284

Review URL: https://codereview.chromium.org/1125133005

Cr-Commit-Position: refs/heads/master@{#330647}