[Payments] Add the pay button, and control its enabled state

components/payments/content/payment_request.h

Index: components/payments/content/payment_request.h
diff --git a/components/payments/content/payment_request.h b/components/payments/content/payment_request.h
index cdecff311a4898320709b775872568c7ce238ec7..b2174ca2b23afc14b056914ac877638b8a945d23 100644
--- a/components/payments/content/payment_request.h
+++ b/components/payments/content/payment_request.h
@@ -60,6 +60,11 @@ class PaymentRequest : payments::mojom::PaymentRequest {
   // such as possibly closing the dialog.
   void OnConnectionTerminated();
 
+  // Called when the user clicks on the "Pay" button.
+  void Pay();
+
+  bool is_ready_to_pay() { return is_ready_to_pay_; }
+
   // Returns the CurrencyFormatter instance for this PaymentRequest.
   // |locale_name| should be the result of the browser's GetApplicationLocale().
   // Note: Having multiple currencies per PaymentRequest is not supported; hence
@@ -128,6 +133,17 @@ class PaymentRequest : payments::mojom::PaymentRequest {
   void PopulateValidatedMethodData(
       const std::vector<payments::mojom::PaymentMethodDataPtr>& method_data);
 
+  // Updates |is_ready_to_pay_| with the current state, by validating that all
+  // the required information is available.
+  void UpdateIsReadyToPay();
+
+  // Returns whether the selected data satisfies the PaymentDetails requirements
+  // (payment methods).
+  bool ArePaymentDetailsSatisfied();
+  // Returns whether the selected data satisfies the PaymentOptions requirements
+  // (contact info, shipping address).
+  bool ArePaymentOptionsSatisfied();
+
   content::WebContents* web_contents_;
   std::unique_ptr<PaymentRequestDelegate> delegate_;
   // |manager_| owns this PaymentRequest.
@@ -135,9 +151,11 @@ class PaymentRequest : payments::mojom::PaymentRequest {
   mojo::Binding<payments::mojom::PaymentRequest> binding_;
   payments::mojom::PaymentRequestClientPtr client_;
   payments::mojom::PaymentDetailsPtr details_;
+  payments::mojom::PaymentOptionsPtr options_;
   std::unique_ptr<CurrencyFormatter> currency_formatter_;
   // A set of supported basic card networks.
   std::vector<std::string> supported_card_networks_;
+  bool is_ready_to_pay_;
 
   // Profiles may change due to (e.g.) sync events, so profiles are cached after
   // loading and owned here. They are populated once only, and ordered by