PaymentApp: Implement InvokePaymentApp() in browser side.

content/browser/service_worker/service_worker_metrics.h

Index: content/browser/service_worker/service_worker_metrics.h
diff --git a/content/browser/service_worker/service_worker_metrics.h b/content/browser/service_worker/service_worker_metrics.h
index 4d229d8567f9b6ba4f0b601363c841eb9ee0a774..6376eb704665c2d47f7357ea62ed18dafc7ace8e 100644
--- a/content/browser/service_worker/service_worker_metrics.h
+++ b/content/browser/service_worker/service_worker_metrics.h
@@ -114,6 +114,7 @@ class ServiceWorkerMetrics {
     // Used when external consumers want to add a request to
     // ServiceWorkerVersion to keep it alive.
     EXTERNAL_REQUEST = 21,
+    PAYMENT_REQUEST = 22,

[nhiroki, 2017/01/12 03:12:38]

This enum is used for UMA, so you also need to update
"ServiceWorkerMetrics.EventType" in tools/metrics/histograms/histograms.xml

[zino, 2017/01/13 16:41:11]

Done.

     // Add new events to record here.
     NUM_TYPES
   };