[Payments] Implement openWindow for service worker based payment handler

content/common/service_worker/service_worker_messages.h

Index: content/common/service_worker/service_worker_messages.h
diff --git a/content/common/service_worker/service_worker_messages.h b/content/common/service_worker/service_worker_messages.h
index ef5a82603f3ad008980345e9460d5ba090865388..6ad80b0dd8c72b122582f6a764685038594ff078 100644
--- a/content/common/service_worker/service_worker_messages.h
+++ b/content/common/service_worker/service_worker_messages.h
@@ -271,8 +271,15 @@ IPC_MESSAGE_ROUTED2(ServiceWorkerHostMsg_SetCachedMetadata,
 // clear the cache associated with |url|.
 IPC_MESSAGE_ROUTED1(ServiceWorkerHostMsg_ClearCachedMetadata, GURL /* url */)
 
-// Ask the browser to open a tab/window (renderer->browser).
-IPC_MESSAGE_ROUTED2(ServiceWorkerHostMsg_OpenWindow,
+// Ask the browser to open a tab/window (renderer->browser) for
+// clients.openWindow.
+IPC_MESSAGE_ROUTED2(ServiceWorkerHostMsg_OpenWindowForClients,
+                    int /* request_id */,
+                    GURL /* url */)
+
+// Ask the browser to open a tab/window (renderer->browser) for payment handler,
+// i.e., PaymentRequestEvent.openWindow().
+IPC_MESSAGE_ROUTED2(ServiceWorkerHostMsg_OpenWindowForPaymentHandler,
                     int /* request_id */,
                     GURL /* url */)