chromeos: Add suspend delay tests for PowerManagerClient.

Add initial unit tests for chromeos::PowerManagerClient's
suspend-delay-handling code. More coming soon.

BUG=646912

Review-Url: https://codereview.chromium.org/2345593002
Cr-Commit-Position: refs/heads/master@{#418716}

chromeos/chromeos.gyp

@@ -417,6 +417,7 @@
       'dbus/fake_power_manager_client_unittest.cc',
       'dbus/gsm_sms_client_unittest.cc',
       'dbus/modem_messaging_client_unittest.cc',
+      'dbus/power_manager_client_unittest.cc',
       'dbus/power_policy_controller_unittest.cc',
       'dbus/services/cros_dbus_service_unittest.cc',
       'dbus/services/proxy_resolution_service_provider_unittest.cc',

chromeos/dbus/power_manager_client.h

@@ -198,6 +198,9 @@ class CHROMEOS_EXPORT PowerManagerClient : public DBusClient {
   ~PowerManagerClient() override;
 
  protected:
+  // Needs to call DBusClient::Init().
+  friend class PowerManagerClientTest;
+
   // Create() should be used instead.
   PowerManagerClient();