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

chrome/browser/ui/views/payments/payment_request_dialog_view.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/views/payments/payment_request_dialog_view.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 125 matching lines @@
 
 void PaymentRequestDialogView::ShowDialog() {
   constrained_window::ShowWebModalDialogViews(this, request_->web_contents());
 }
 
 void PaymentRequestDialogView::CloseDialog() {
   // This calls PaymentRequestDialogView::Cancel() before closing.
   GetWidget()->Close();
 }
 
+void PaymentRequestDialogView::UpdatePayButtonState(bool enabled) {

[anthonyvd, 2017/02/28 17:16:32]

I don't think this pattern is the way to go:

1. The Payment Sheet isn't the only one with a pay button
2. Multiple Sheets layered on top of each other might need to update their pay
button at the same time
3. Traversing the view hierarchy isn't expensive but it's also not free.
4. As your comment mentions, there are weird states where the dialog is closed
and PR calls this function

I would instead add an PaymentRequest::Observer that raises a
PaymentInformationChanged() event. View controllers can query PaymentRequest in
their implementation of the observer to determine the state of the pay button
and subscribe/unsubscribe themselves to avoid lifetime issues.

WDYT?

[Mathieu, 2017/02/28 19:42:39]

OMG yes, it's much better with observers. Good catch about the pay button on
multiple screens, too. 

+  // It's theoretically possible that the dialog is closed and PaymentRequest
+  // still calls this.
+  if (payment_sheet_view_)
+    return;
+
+  const auto it = controller_map_.find(payment_sheet_view_);
+  DCHECK(it != controller_map_.end());
+  PaymentSheetViewController* sheet_controller =
+      static_cast<PaymentSheetViewController*>(it->second.get());
+  sheet_controller->UpdatePayButtonState(enabled);
+}
+
 void PaymentRequestDialogView::ShowInitialPaymentSheet() {
-  view_stack_.Push(
-      CreateViewAndInstallController(
-          base::MakeUnique<PaymentSheetViewController>(request_, this),
-          &controller_map_),
-      /* animate = */ false);
+  std::unique_ptr<views::View> sheet_view = CreateViewAndInstallController(
+      base::MakeUnique<PaymentSheetViewController>(request_, this),
+      &controller_map_);
+  payment_sheet_view_ = sheet_view.get();
+  view_stack_.Push(std::move(sheet_view), /* animate = */ false);
   if (observer_for_testing_)
     observer_for_testing_->OnDialogOpened();
 }
 
 gfx::Size PaymentRequestDialogView::GetPreferredSize() const {
   return gfx::Size(450, 450);
 }
 
 void PaymentRequestDialogView::ViewHierarchyChanged(
     const ViewHierarchyChangedDetails& details) {
   // When a view that is associated with a controller is removed from this
   // view's descendants, dispose of the controller.
   if (!details.is_add &&
       controller_map_.find(details.child) != controller_map_.end()) {
     DCHECK(!details.move_view);
+    if (details.child == payment_sheet_view_)
+      payment_sheet_view_ = nullptr;
+
     controller_map_.erase(details.child);
   }
 }
 
 }  // namespace payments