Refactor GestureNavigation to eliminate code redundancy

content/browser/web_contents/aura/overscroll_window_animation.h

Index: content/browser/web_contents/aura/overscroll_window_animation.h
diff --git a/content/browser/web_contents/aura/overscroll_window_animation.h b/content/browser/web_contents/aura/overscroll_window_animation.h
new file mode 100644
index 0000000000000000000000000000000000000000..93be76cbe12e9a096549cfd792781b6f1b5532fd
--- /dev/null
+++ b/content/browser/web_contents/aura/overscroll_window_animation.h
@@ -0,0 +1,119 @@
+// 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 animation of a window sliding on top or behind another one. The
+// main window, which is the one displayed before the animation starts, is not
+// owned by OverscrollWindowAnimation, while the slide window, created at the
+// start of the animation, is owned by us for its duration.
+class CONTENT_EXPORT OverscrollWindowAnimation
+    : public OverscrollControllerDelegate,
+      ui::ImplicitAnimationObserver {
+ public:
+  // The direction of this animation. SLIDE_FRONT indicates that the main window
+  // stays still while the slide window moves on top of it, entering in from the
+  // right. SLIDE_BACK means that the main window is animated to the right,
+  // revealing the slide  window in the back, which stays still. SLIDE_NONE
+  // means we are not animating yet. Left and right are reversed for RTL
+  // languages, but stack order remains unchanged.
+  enum Direction { SLIDE_FRONT, SLIDE_BACK, SLIDE_NONE };
+
+  // Delegate class that interfaces with the window animation.
+  class CONTENT_EXPORT Delegate {
+   public:
+    virtual ~Delegate() {}
+
+    // The following two functions create a slide window.

[sadrul, 2015/04/07 17:10:08]

This comment isn't necessary.

[Nina, 2015/04/07 19:08:56]

Removed.

+    virtual scoped_ptr<aura::Window> CreateFrontWindow() = 0;
+    virtual scoped_ptr<aura::Window> CreateBackWindow() = 0;
+
+    // Returns the main window that participates in the animation. We do not own
+    // this window.

[sadrul, 2015/04/07 17:10:08]

Not clear what 'We' here means. Either 'The delegate does not own this window'
or 'The caller does not own the window'.

[Nina, 2015/04/07 19:08:56]

Good call. s/ to The delegate does not own this window

+    virtual aura::Window* GetMainWindow() const = 0;
+
+    // Called when we know the animation is going to complete successfully, but
+    // before it actually completes.
+    virtual void OnOverscrollCompleting() = 0;
+
+    // Called when the animation has been completed.
+    virtual void OnOverscrollCompleted(scoped_ptr<aura::Window> window) = 0;

[sadrul, 2015/04/07 17:10:08]

What is |window|?

[Nina, 2015/04/07 19:08:56]

Added "The slide window is transferred to the delegate."

+
+    // Called when the overscroll gesture has been cancelled, after the cancel
+    // animation finishes.
+    virtual void OnOverscrollCancelled() = 0;
+  };
+
+  explicit OverscrollWindowAnimation(Delegate* delegate);
+
+  ~OverscrollWindowAnimation() override;
+
+  // Returns true if we are currently animating.
+  bool is_active() const { return !!slide_window_; }
+
+  // Overridden from OverscrollControllerDelegate:

[sadrul, 2015/04/07 17:10:08]

// OverscrollControllerDelegate:

(like below for ImplicitAnimationObserver)

[Nina, 2015/04/07 19:08:56]

Done.

+  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:
+  // Cancels the animation, animating the front window to its original position.
+  void CancelAnimation();
+
+  // 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 animation.
+  ui::Layer* GetFrontLayer() const;

[sadrul, 2015/04/07 17:10:08]

Document ownership of the returned layer. If the caller owns this layer, then
return a scoped_ptr<>

[Nina, 2015/04/07 19:08:56]

The caller does not own it, made it clear in the comment.

+
+  // ui::ImplicitAnimationObserver:
+  void OnImplicitAnimationsCompleted() override;
+
+  // We own the window created for the animation.
+  scoped_ptr<aura::Window> slide_window_;
+
+  // Shadow shown under the animated layer.
+  scoped_ptr<ShadowLayerDelegate> shadow_;
+
+  // Delegate that provides the animation target and is notified of the
+  // animation state.
+  Delegate* delegate_;
+
+  // The current animation direction.
+  Direction direction_;
+
+  // Indicates if the current animation has been cancelled. True while the
+  // cancel animation is in progress.
+  bool overscroll_cancelled_;

[sadrul, 2015/04/07 17:10:08]

DISALLOW_COPY_AND_ASSIGN

[Nina, 2015/04/07 19:08:56]

Done.

+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_WEB_CONTENTS_AURA_OVERSCROLL_WINDOW_ANIMATION_H_