chromeos: Make CheckIdleStateIsLocked() query D-Bus client.

chromeos/dbus/fake_session_manager_client.cc

Index: chromeos/dbus/fake_session_manager_client.cc
diff --git a/chromeos/dbus/fake_session_manager_client.cc b/chromeos/dbus/fake_session_manager_client.cc
index f16e9c612595a58b6b8d8202387a2ae166d8e7e9..27fe2df2bf1ec0eaa04b1b469378b23a65e959e2 100644
--- a/chromeos/dbus/fake_session_manager_client.cc
+++ b/chromeos/dbus/fake_session_manager_client.cc
@@ -39,6 +39,10 @@ bool FakeSessionManagerClient::HasObserver(const Observer* observer) const {
   return observers_.HasObserver(observer);
 }
 
+bool FakeSessionManagerClient::IsScreenLocked() const {
+  return false;
+}
+
 void FakeSessionManagerClient::EmitLoginPromptVisible() {
 }