Implement finding BLE connections in chrome://proximity-auth.

components/proximity_auth/ble/bluetooth_low_energy_connection_finder.h

Index: components/proximity_auth/ble/bluetooth_low_energy_connection_finder.h
diff --git a/components/proximity_auth/ble/bluetooth_low_energy_connection_finder.h b/components/proximity_auth/ble/bluetooth_low_energy_connection_finder.h
index 5d4cc52473d04d24caec269bb6bc2b25bbc39650..9c76a48e04c3abbe0441f59b22e9d62f319ac8d8 100644
--- a/components/proximity_auth/ble/bluetooth_low_energy_connection_finder.h
+++ b/components/proximity_auth/ble/bluetooth_low_energy_connection_finder.h
@@ -98,6 +98,10 @@ class BluetoothLowEnergyConnectionFinder
   // Restarts the discovery session after creating |connection_| fails.
   void RestartDiscoverySessionWhenReady();
 
+  // Used to invoke |connection_callback_| asynchronously, decoupling the
+  // callback invocation from the ConnectionObserver callstack.
+  void InvokeCallbackAsync();
+
   // Returns the device with |device_address|.
   device::BluetoothDevice* GetDevice(std::string device_address);