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

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

Index: chrome/browser/ui/views/payments/payment_request_dialog_view.cc
diff --git a/chrome/browser/ui/views/payments/payment_request_dialog_view.cc b/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
index d6a122e5ad73950e18d6ad7ab4cffd4a46c5285c..c84a20a22cc786af0dc31d39d2e108b00178644e 100644
--- a/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
+++ b/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
@@ -143,12 +143,25 @@ void PaymentRequestDialogView::CloseDialog() {
   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();
 }
@@ -164,6 +177,9 @@ void PaymentRequestDialogView::ViewHierarchyChanged(
   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);
   }
 }