Add DBus plumbing and tests for sending devices with ATT read/writes.

device/bluetooth/test/test_bluetooth_local_gatt_service_delegate.cc

Index: device/bluetooth/test/test_bluetooth_local_gatt_service_delegate.cc
diff --git a/device/bluetooth/test/test_bluetooth_local_gatt_service_delegate.cc b/device/bluetooth/test/test_bluetooth_local_gatt_service_delegate.cc
index b1970646fe1087c2391672f556d95680c5e6d6e5..aa306ca34bb86eacfafe664fe69eb584b0030895 100644
--- a/device/bluetooth/test/test_bluetooth_local_gatt_service_delegate.cc
+++ b/device/bluetooth/test/test_bluetooth_local_gatt_service_delegate.cc
@@ -31,6 +31,7 @@ void TestBluetoothLocalGattServiceDelegate::OnCharacteristicReadRequest(
     error_callback.Run();
     return;
   }
+  last_seen_device_ = device->GetIdentifier();
   callback.Run(BluetoothGattServerTest::GetValue(value_to_write_));
 }
 
@@ -47,6 +48,7 @@ void TestBluetoothLocalGattServiceDelegate::OnCharacteristicWriteRequest(
     error_callback.Run();
     return;
   }
+  last_seen_device_ = device->GetIdentifier();
   last_written_value_ = BluetoothGattServerTest::GetInteger(value);
   callback.Run();
 }
@@ -62,6 +64,7 @@ void TestBluetoothLocalGattServiceDelegate::OnDescriptorReadRequest(
     error_callback.Run();
     return;
   }
+  last_seen_device_ = device->GetIdentifier();
   callback.Run(BluetoothGattServerTest::GetValue(value_to_write_));
 }
 
@@ -77,6 +80,7 @@ void TestBluetoothLocalGattServiceDelegate::OnDescriptorWriteRequest(
     error_callback.Run();
     return;
   }
+  last_seen_device_ = device->GetIdentifier();
   last_written_value_ = BluetoothGattServerTest::GetInteger(value);
   callback.Run();
 }