[WebPayments] Implement state transitions in desktop WebPayments dialog.

chrome/browser/ui/views/payments/view_stack.h

+// 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.
+
+#ifndef CHROME_BROWSER_UI_VIEWS_PAYMENTS_VIEW_STACK_H_
+#define CHROME_BROWSER_UI_VIEWS_PAYMENTS_VIEW_STACK_H_
+
+#include "ui/views/view.h"
+#include "ui/views/animation/bounds_animator.h"
+#include "ui/views/animation/bounds_animator_observer.h"
+
+// This view represents a stack of views that slide in over one another from
+// left to right. It manages the animation and lifetime of views that are
+// pushed and popped on it. To use this class, add it to a view hierarchy, and
+// call Push/Pop to animate views in and out.
+class ViewStack : public views::BoundsAnimatorObserver,
+                  public views::View {
+ public:
+  explicit ViewStack(std::unique_ptr<views::View> initial_view);

[sky, 2016/12/12 17:38:07]

Can you make the constructor take no args and instead consumers call Push when
ready? I think it makes for a simpler API, with less code duplication (for
example, you forgot the set_owned_by_client for the view passed to the
constructor). 

[anthonyvd, 2016/12/12 18:47:57]

Done, good point. To avoid the situation where the first view animates on top of
an empty space, I added the |animate| param to Push(). This allows callers to
push a view without the animation. 

+  ~ViewStack() override;
+
+  // Adds a view to the stack and starts animating it in from the right. This
+  // takes ownership of the view and calls set_owned_by_client() on it.
+  void Push(std::unique_ptr<views::View> state);
+
+  // Removes a view from the stack, animates it out of view, and makes sure
+  // it's properly deleted after the animation.
+  void Pop();
+
+  // views::View:
+  // The children of this view must not be able to process events when the views
+  // are being animated so this returns false when an animation is in progress.
+  bool CanProcessEventsWithinSubtree() const override;
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(
+      ViewStackTest, TestPopStateRemovesChildViewAndCleansUpState);
+
+  FRIEND_TEST_ALL_PREFIXES(ViewStackTest, TestDeletingViewCleansUpState);
+
+  // Returns the top state of the stack, used in tests.
+  views::View* top() { return stack_.top().get(); }
+
+  // views::BoundsAnimatorObserver:
+  void OnBoundsAnimatorProgressed(views::BoundsAnimator* animator) override {}
+  void OnBoundsAnimatorDone(views::BoundsAnimator* animator) override;
+
+  std::stack<std::unique_ptr<views::View>> stack_;
+
+  std::unique_ptr<views::BoundsAnimator> slide_in_animator_;
+  std::unique_ptr<views::BoundsAnimator> slide_out_animator_;
+
+  bool can_process_events_within_subtree_;

[sky, 2016/12/12 17:38:08]

Does the value of this always match that of whether an animation is running? Can
it be removed and instead check the animations (less duplication means smaller
possibility of getting things out of sync).

[anthonyvd, 2016/12/12 18:47:57]

It does, good catch! Done.

+
+  DISALLOW_COPY_AND_ASSIGN(ViewStack);
+};
+
+#endif  // CHROME_BROWSER_UI_VIEWS_PAYMENTS_VIEW_STACK_H_