PaymentApp: Implement PaymentAppProvider for LayoutTest.

components/test_runner/web_test_delegate.h

Index: components/test_runner/web_test_delegate.h
diff --git a/components/test_runner/web_test_delegate.h b/components/test_runner/web_test_delegate.h
index 2cdbefa9e164c607958c073e9c04eef227e0451c..329191b6dc73be1da242cc0e11ebe129139d9ece 100644
--- a/components/test_runner/web_test_delegate.h
+++ b/components/test_runner/web_test_delegate.h
@@ -202,6 +202,11 @@ class WebTestDelegate {
   virtual void SendBluetoothManualChooserEvent(const std::string& event,
                                                const std::string& argument) = 0;
 
+  virtual void GetAllPaymentAppIDs(
+      const base::Callback<void(const std::vector<int64_t>&)>& callback) = 0;
+
+  virtual void InvokePaymentApp(int64_t registration_id) = 0;
+
   // Controls which WebView should be focused.
   virtual void SetFocus(blink::WebView* web_view, bool focus) = 0;