[agent] Ignore deprecation lint warning for AgentImpl usage

To prepare for AgentImpl deprecation

Test: compiles
Change-Id: Ifc13f8c002d5bd871f6760ff8ea79ec815075755
diff --git a/bin/xi/xi_session_agent/lib/main.dart b/bin/xi/xi_session_agent/lib/main.dart
index f02ddf6..11416b7 100644
--- a/bin/xi/xi_session_agent/lib/main.dart
+++ b/bin/xi/xi_session_agent/lib/main.dart
@@ -28,6 +28,9 @@
   PendingNotification(this.method, this.params);
 }
 
+
+/// TODO: Refactor this class to use the new SDK instead of deprecated API
+/// ignore: deprecated_member_use
 class XiSessionAgent extends AgentImpl {
   final _xiSessionManager = XiSessionManagerImpl();
 
diff --git a/examples/tictactoe/bin/tictactoe/game_tracker_agent/lib/src/agent.dart b/examples/tictactoe/bin/tictactoe/game_tracker_agent/lib/src/agent.dart
index bed910a..47127f8 100644
--- a/examples/tictactoe/bin/tictactoe/game_tracker_agent/lib/src/agent.dart
+++ b/examples/tictactoe/bin/tictactoe/game_tracker_agent/lib/src/agent.dart
@@ -13,6 +13,9 @@
 import 'game_tracker_impl.dart';
 
 /// An implementation of the [Agent] interface for tracking game wins.
+/// 
+/// TODO: Refactor this class to use the new SDK instead of deprecated API
+/// ignore: deprecated_member_use
 class GameTrackerAgent extends AgentImpl {
   GameTrackerAgent({@required StartupContext startupContext})
       : super(startupContext: startupContext);
diff --git a/public/lib/agent/dart/lib/src/agent_impl.dart b/public/lib/agent/dart/lib/src/agent_impl.dart
index 1e81bbd..4750a49 100644
--- a/public/lib/agent/dart/lib/src/agent_impl.dart
+++ b/public/lib/agent/dart/lib/src/agent_impl.dart
@@ -17,6 +17,7 @@
 
 /// A base class for implementing an [Agent] which receives common services and
 /// also helps exposing services through an outgoing [ServiceProvider].
+@Deprecated('Use package:fuchsia_modular/agent.dart instead')
 abstract class AgentImpl implements Agent, Lifecycle {
   final AgentBinding _agentBinding = new AgentBinding();
   final LifecycleBinding _lifecycleBinding = new LifecycleBinding();
diff --git a/shell/agents/home_work_agent/lib/main.dart b/shell/agents/home_work_agent/lib/main.dart
index 69668d5..b670376 100644
--- a/shell/agents/home_work_agent/lib/main.dart
+++ b/shell/agents/home_work_agent/lib/main.dart
@@ -16,6 +16,9 @@
 HomeWorkAgent _agent;
 
 /// An implementation of the [Agent] interface.
+/// 
+/// TODO: Refactor this class to use the new SDK instead of deprecated API
+/// ignore: deprecated_member_use
 class HomeWorkAgent extends AgentImpl {
   final IntelligenceServicesProxy _intelligenceServices =
       new IntelligenceServicesProxy();