Verify behavior of PaymentRequest.show() method, part 1.

components/payments/content/payment_request_web_contents_manager.h

Index: components/payments/content/payment_request_web_contents_manager.h
diff --git a/components/payments/content/payment_request_web_contents_manager.h b/components/payments/content/payment_request_web_contents_manager.h
index be08a3da0035226eb91044d9d85b61fd37c81ff8..6918520a9bf41ca10be847b02d0551cb2a90ed02 100644
--- a/components/payments/content/payment_request_web_contents_manager.h
+++ b/components/payments/content/payment_request_web_contents_manager.h
@@ -50,6 +50,10 @@ class PaymentRequestWebContentsManager
   // Destroys the given |request|.
   void DestroyRequest(PaymentRequest* request);
 
+  // Called when |request| has received the show() call. Returns true if the
+  // |request| can be shown. (Only one request at a time can be shown per tab.)
+  bool CanShow(PaymentRequest* request);
+
  private:
   explicit PaymentRequestWebContentsManager(content::WebContents* web_contents);
   friend class content::WebContentsUserData<PaymentRequestWebContentsManager>;
@@ -62,6 +66,10 @@ class PaymentRequestWebContentsManager
   std::unordered_map<PaymentRequest*, std::unique_ptr<PaymentRequest>>
       payment_requests_;
 
+  // The currently displayed instance of PaymentRequest. Points to one of the
+  // elements in payment_requests_. Can be null.
+  PaymentRequest* showing_;
+
   DISALLOW_COPY_AND_ASSIGN(PaymentRequestWebContentsManager);
 };