PaymentApp: Implement PaymentAppManager.setManifest().

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 0d406b79629616b651fdf4a8b18ebf2f70232e96..d78c2d9ffcd928296398dba43b13306aaf219431 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -1134,6 +1134,7 @@ test("content_unittests") {
     "../browser/notifications/notification_id_generator_unittest.cc",
     "../browser/notifications/platform_notification_context_unittest.cc",
     "../browser/notifications/type_converters_unittest.cc",
+    "../browser/payments/payment_app_manager_unittest.cc",
     "../browser/presentation/presentation_service_impl_unittest.cc",
     "../browser/presentation/presentation_type_converters_unittest.cc",
     "../browser/quota/mock_quota_manager.cc",
@@ -1367,6 +1368,7 @@ test("content_unittests") {
     "//cc/ipc",
     "//cc/surfaces",
     "//components/display_compositor",
+    "//components/payments:payment_app",
     "//content:resources",
     "//content/app:both_for_content_tests",
     "//content/browser:for_content_tests",