Refactor GestureNavigation to eliminate code redundancy

content/browser/web_contents/aura/overscroll_window_animation.h

+// Copyright 2015 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 CONTENT_BROWSER_WEB_CONTENTS_AURA_OVERSCROLL_WINDOW_ANIMATION_H_
+#define CONTENT_BROWSER_WEB_CONTENTS_AURA_OVERSCROLL_WINDOW_ANIMATION_H_
+
+#include "base/gtest_prod_util.h"
+#include "content/browser/renderer_host/overscroll_controller_delegate.h"
+#include "content/common/content_export.h"
+#include "ui/compositor/layer_animation_observer.h"
+
+namespace aura {
+class Window;
+}
+
+namespace ui {
+class Layer;
+class LayerAnimator;
+}
+
+namespace content {
+
+class ShadowLayerDelegate;
+class WebContentsImpl;
+
+// Manages the animations during an overscroll navigation by handling overscroll

[mfomitchev, 2015/03/26 15:36:00]

We probably shouldn't be talking about "navigation" in the context of this
class. This class is all about animations in response to overscroll events. It
doesn't have to know or care that these animations are happening as the visual
candy associated with navigations.
More generally, when designing a class, we should try to establish as "broad"
role for it as possible. This way we minimize the change that when outside
components change we will have to change the class. Thus when we write comments
(or name class members) we should also look at it from the view of the "broad"
role of the class. It's tempting to comment in terms of the specific use case
that the class is being used for, but generally speaking that should be avoided.

[Nina, 2015/03/27 17:52:36]

Changed the comment completely. Check it out.

+// events.
+class CONTENT_EXPORT OverscrollWindowAnimation
+    : public OverscrollControllerDelegate,
+      ui::ImplicitAnimationObserver {
+ public:
+  enum Direction { SLIDE_FRONT, SLIDE_BACK, SLIDE_NONE };
+
+  // Delegate class that interfaces with the window animation, responsible for
+  // navigation.
+  class Delegate {
+   public:
+    virtual ~Delegate() {}
+
+    // The following two functions create a slide window and transfer back its
+    // ownership.
+    virtual scoped_ptr<aura::Window> CreateFrontWindow() = 0;
+    virtual scoped_ptr<aura::Window> CreateBackWindow() = 0;
+
+    // Returns the live window that participates in the overscroll gesture.
+    virtual aura::Window* GetTargetWindow() const = 0;

[mfomitchev, 2015/03/26 02:41:39]

"Target window" doesn't really explain what this window is. Nor does the comment
really. Try to explain it from the POV of OWA. Perhaps GetMainWindow() or
GetOwnerWindow(). The role of this window and window_ can be establishedin the
comments to the OWA class itself if that makes sense

[Nina, 2015/03/27 17:52:36]

Changed to GetMainWindow.

+
+    // Called when we know the animation is going to complete successfully.
+    virtual void OnOverscrollCompleting() = 0;
+
+    // Called when the animation has been completed.
+    virtual void OnOverscrollCompleted(scoped_ptr<aura::Window> window) = 0;
+
+    // Called when the overscroll gesture has been aborted.
+    virtual void OnOverscrollAborted() = 0;
+  };
+
+  explicit OverscrollWindowAnimation(Delegate* delegate);
+
+  ~OverscrollWindowAnimation() override;
+
+  // Returns true if we are currently handling a slide animation.
+  bool is_active() const { return !!window_; }
+
+  // Overridden from OverscrollControllerDelegate:
+  gfx::Rect GetVisibleBounds() const override;
+
+  bool OnOverscrollUpdate(float delta_x, float delta_y) override;
+
+  void OnOverscrollComplete(OverscrollMode overscroll_mode) override;
+
+  void OnOverscrollModeChange(OverscrollMode old_mode,
+                              OverscrollMode new_mode) override;
+
+ private:
+  /*friend class OverscrollWindowAnimationTest;
+  FRIEND_TEST_ALL_PREFIXES(OverscrollWindowAnimationTest,
+                           BasicOverscroll);*/
+
+  // Starts the overscroll cancelled animation.
+  void CancelOverscroll();
+
+  // Moves the animated window according to the given scroll deltas. Returns
+  // true if the update moved the window.
+  bool UpdateForScroll(float delta_x);
+
+  // Returns a translation on the x axis for the given overscroll.
+  float GetTranslationForOverscroll(float delta_x);
+
+  // Returns the layer that is animated for the overscroll gesture.
+  ui::Layer* GetFrontLayer() const;
+
+  // ui::ImplicitAnimationObserver:
+  void OnImplicitAnimationsCompleted() override;
+
+  // Owns the new window created on the overscroll gesture.
+  scoped_ptr<aura::Window> window_;
+
+  // Shadow shown under the animated layer.
+  scoped_ptr<ShadowLayerDelegate> shadow_;
+
+  // Delegate that provides the animation target and handles navigation.
+  Delegate* delegate_;
+
+  // The current overscroll direction.
+  Direction direction_;
+
+  // Indicates if the current overscroll gesture has been cancelled.
+  bool overscroll_cancelled_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_WEB_CONTENTS_AURA_OVERSCROLL_WINDOW_ANIMATION_H_