Split Screen mode implementation.

Implements Split Screen mode and window cycling behavior.
Resubmit of https://codereview.chromium.org/420603011/

TBR=oshima@chromium.org,mukai@chromium.org

BUG=383421

Review URL: https://codereview.chromium.org/468133002

Cr-Commit-Position: refs/heads/master@{#289392}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289392 0039d316-1c4b-4281-b951-d872f2087c98

12 files changed, 561 insertions, 92 deletions

diff --git a/athena/wm/bezel_controller.cc b/athena/wm/bezel_controller.cc
index fb62155..a4e8156 100644
--- a/athena/wm/bezel_controller.cc
+++ b/athena/wm/bezel_controller.cc
@@ -6,6 +6,10 @@
 
 #include "ui/aura/window.h"
 #include "ui/events/event_handler.h"
+#include "ui/gfx/display.h"
+#include "ui/gfx/geometry/point_conversions.h"
+#include "ui/gfx/screen.h"
+#include "ui/wm/core/coordinate_conversion.h"
 
 namespace athena {
 namespace {
@@ -15,7 +19,7 @@ namespace {
 // So setting this width fairly high for now.
 const float kBezelWidth = 20.0f;
 
-const float kScrollPositionNone = -100;
+const float kScrollDeltaNone = 0;
 
 bool ShouldProcessGesture(ui::EventType event_type) {
   return event_type == ui::ET_GESTURE_SCROLL_UPDATE ||
@@ -24,6 +28,24 @@ bool ShouldProcessGesture(ui::EventType event_type) {
          event_type == ui::ET_GESTURE_END;
 }
 
+gfx::Display GetDisplay(aura::Window* window) {
+  gfx::Screen* screen = gfx::Screen::GetScreenFor(window);
+  return screen->GetDisplayNearestWindow(window);
+}
+
+float GetDistance(const gfx::PointF& location,
+                  aura::Window* window,
+                  BezelController::Bezel bezel) {
+  DCHECK(bezel == BezelController::BEZEL_LEFT ||
+         bezel == BezelController::BEZEL_RIGHT);
+  // Convert location from window coordinates to screen coordinates.
+  gfx::Point point_in_screen(gfx::ToRoundedPoint(location));
+  wm::ConvertPointToScreen(window, &point_in_screen);
+  return bezel == BezelController::BEZEL_LEFT
+             ? point_in_screen.x()
+             : point_in_screen.x() - GetDisplay(window).bounds().width();
+}
+
 }  // namespace
 
 BezelController::BezelController(aura::Window* container)
@@ -34,25 +56,22 @@ BezelController::BezelController(aura::Window* container)
       left_right_delegate_(NULL) {
 }
 
-float BezelController::GetDistance(const gfx::PointF& position,
-                                   BezelController::Bezel bezel) {
-  DCHECK(bezel == BEZEL_LEFT || bezel == BEZEL_RIGHT);
-  return bezel == BEZEL_LEFT
-             ? position.x()
-             : position.x() - container_->GetBoundsInScreen().width();
+void BezelController::SetState(BezelController::State state) {
+  // Use SetState(State, float) if |state| is one of the BEZEL_SCROLLING states.
+  DCHECK_NE(state, BEZEL_SCROLLING_TWO_FINGERS);
+  DCHECK_NE(state, BEZEL_SCROLLING_ONE_FINGER);
+  SetState(state, kScrollDeltaNone);
 }
 
 void BezelController::SetState(BezelController::State state,
-                               const gfx::PointF& scroll_position) {
+                               float scroll_delta) {
   if (!left_right_delegate_ || state == state_)
     return;
 
-  if (state == BEZEL_SCROLLING_TWO_FINGERS) {
-    float delta = GetDistance(scroll_position, scroll_bezel_);
-    left_right_delegate_->ScrollBegin(scroll_bezel_, delta);
-  } else if (state_ == BEZEL_SCROLLING_TWO_FINGERS) {
+  if (state == BEZEL_SCROLLING_TWO_FINGERS)
+    left_right_delegate_->ScrollBegin(scroll_bezel_, scroll_delta);
+  else if (state_ == BEZEL_SCROLLING_TWO_FINGERS)
     left_right_delegate_->ScrollEnd();
-  }
   state_ = state;
   if (state == NONE) {
     scroll_bezel_ = BEZEL_NONE;
@@ -62,10 +81,10 @@ void BezelController::SetState(BezelController::State state,
 
 // Only implemented for LEFT and RIGHT bezels ATM.
 BezelController::Bezel BezelController::GetBezel(const gfx::PointF& location) {
+  int screen_width = GetDisplay(container_).bounds().width();
   if (location.x() < kBezelWidth) {
     return BEZEL_LEFT;
-  } else if (location.x() >
-             container_->GetBoundsInScreen().width() - kBezelWidth) {
+  } else if (location.x() > screen_width - kBezelWidth) {
     return BEZEL_RIGHT;
   } else {
     return BEZEL_NONE;
@@ -73,7 +92,7 @@ BezelController::Bezel BezelController::GetBezel(const gfx::PointF& location) {
 }
 
 void BezelController::OnGestureEvent(ui::GestureEvent* event) {
-  // TODO (mfomitchev): Currently we aren't retargetting or consuming any of the
+  // TODO(mfomitchev): Currently we aren't retargetting or consuming any of the
   // touch events. This means that content can prevent the generation of gesture
   // events and two-finger scroll won't work. Possible solution to this problem
   // is hosting our own gesture recognizer or retargetting touch events at the
@@ -92,11 +111,15 @@ void BezelController::OnGestureEvent(ui::GestureEvent* event) {
   const gfx::PointF& event_location = event->location_f();
   const ui::GestureEventDetails& event_details = event->details();
   int num_touch_points = event_details.touch_points();
+  float scroll_delta = kScrollDeltaNone;
+  if (scroll_bezel_ != BEZEL_NONE) {
+    aura::Window* target_window = static_cast<aura::Window*>(event->target());
+    scroll_delta = GetDistance(event_location, target_window, scroll_bezel_);
+  }
 
   if (type == ui::ET_GESTURE_BEGIN) {
     if (num_touch_points > 2) {
-      SetState(IGNORE_CURRENT_SCROLL,
-               gfx::Point(kScrollPositionNone, kScrollPositionNone));
+      SetState(IGNORE_CURRENT_SCROLL);
       return;
     }
     BezelController::Bezel event_bezel = GetBezel(event->location_f());
@@ -104,12 +127,10 @@ void BezelController::OnGestureEvent(ui::GestureEvent* event) {
       case NONE:
         scroll_bezel_ = event_bezel;
         scroll_target_ = event->target();
-        if (event_bezel != BEZEL_LEFT && event_bezel != BEZEL_RIGHT) {
-          SetState(IGNORE_CURRENT_SCROLL,
-                   gfx::Point(kScrollPositionNone, kScrollPositionNone));
-        } else {
-          SetState(BEZEL_GESTURE_STARTED, event_location);
-        }
+        if (event_bezel != BEZEL_LEFT && event_bezel != BEZEL_RIGHT)
+          SetState(IGNORE_CURRENT_SCROLL);
+        else
+          SetState(BEZEL_GESTURE_STARTED);
         break;
       case IGNORE_CURRENT_SCROLL:
         break;
@@ -120,12 +141,11 @@ void BezelController::OnGestureEvent(ui::GestureEvent* event) {
         DCHECK_NE(scroll_bezel_, BEZEL_NONE);
 
         if (event_bezel != scroll_bezel_) {
-          SetState(IGNORE_CURRENT_SCROLL,
-                   gfx::Point(kScrollPositionNone, kScrollPositionNone));
+          SetState(IGNORE_CURRENT_SCROLL);
           return;
         }
         if (state_ == BEZEL_SCROLLING_ONE_FINGER)
-          SetState(BEZEL_SCROLLING_TWO_FINGERS, event_location);
+          SetState(BEZEL_SCROLLING_TWO_FINGERS);
         break;
       case BEZEL_SCROLLING_TWO_FINGERS:
         // Should've exited above
@@ -138,10 +158,9 @@ void BezelController::OnGestureEvent(ui::GestureEvent* event) {
 
     CHECK(scroll_target_);
     if (num_touch_points == 1) {
-      SetState(NONE, gfx::Point(kScrollPositionNone, kScrollPositionNone));
+      SetState(NONE);
     } else {
-      SetState(IGNORE_CURRENT_SCROLL,
-               gfx::Point(kScrollPositionNone, kScrollPositionNone));
+      SetState(IGNORE_CURRENT_SCROLL);
     }
   } else if (type == ui::ET_GESTURE_SCROLL_BEGIN) {
     DCHECK(state_ == IGNORE_CURRENT_SCROLL || state_ == BEZEL_GESTURE_STARTED);
@@ -149,19 +168,18 @@ void BezelController::OnGestureEvent(ui::GestureEvent* event) {
       return;
 
     if (num_touch_points == 1) {
-      SetState(BEZEL_SCROLLING_ONE_FINGER, event_location);
+      SetState(BEZEL_SCROLLING_ONE_FINGER, scroll_delta);
       return;
     }
 
     DCHECK_EQ(num_touch_points, 2);
-    SetState(BEZEL_SCROLLING_TWO_FINGERS, event_location);
+    SetState(BEZEL_SCROLLING_TWO_FINGERS, scroll_delta);
     if (left_right_delegate_->CanScroll())
       event->SetHandled();
   } else if (type == ui::ET_GESTURE_SCROLL_UPDATE) {
     if (state_ != BEZEL_SCROLLING_TWO_FINGERS)
       return;
 
-    float scroll_delta = GetDistance(event_location, scroll_bezel_);
     left_right_delegate_->ScrollUpdate(scroll_delta);
     if (left_right_delegate_->CanScroll())
       event->SetHandled();
diff --git a/athena/wm/bezel_controller.h b/athena/wm/bezel_controller.h
index 30fe974..7bec71a 100644
--- a/athena/wm/bezel_controller.h
+++ b/athena/wm/bezel_controller.h
@@ -35,12 +35,15 @@ class BezelController : public ui::EventHandler {
     virtual ~ScrollDelegate() {}
 
     // Beginning of a bezel scroll gesture started from the |bezel|.
+    // |delta| is the difference between the x-coordinate of the current scroll
+    // position and the bezel. It will be zero or negative for the right bezel.
     virtual void ScrollBegin(Bezel bezel, float delta) = 0;
 
     // End of the current bezel scroll
     virtual void ScrollEnd() = 0;
 
     // Update of the scroll position for the currently active bezel scroll.
+    // |delta| has the same meaning as in ScrollBegin().
     virtual void ScrollUpdate(float delta) = 0;
 
     // Should return false if the delegate isn't going to react to the scroll
@@ -67,11 +70,10 @@ class BezelController : public ui::EventHandler {
     BEZEL_SCROLLING_TWO_FINGERS,
   };
 
-  // Calculates the distance from |position| to the |bezel|.
-  float GetDistance(const gfx::PointF& position, Bezel bezel);
-
-  // |scroll_position| only needs to be passed in the scrolling state
-  void SetState(State state, const gfx::PointF& scroll_position);
+  void SetState(State state);
+  // |scroll_delta| only needs to be passed when |state| is one of the
+  // BEZEL_SROLLING states.
+  void SetState(State state, float scroll_delta);
 
   // Returns the bezel corresponding to the |location| or BEZEL_NONE if the
   // location is outside of the bezel area.
diff --git a/athena/wm/mru_window_tracker.cc b/athena/wm/mru_window_tracker.cc
new file mode 100644
index 0000000..b2cda0c
--- /dev/null
+++ b/athena/wm/mru_window_tracker.cc
@@ -0,0 +1,53 @@
+// Copyright 2014 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 "athena/wm/mru_window_tracker.h"
+
+#include "ui/aura/window.h"
+
+namespace athena {
+
+MruWindowTracker::MruWindowTracker(aura::Window* container)
+    : container_(container) {
+  container->AddObserver(this);
+}
+
+MruWindowTracker::~MruWindowTracker() {
+  if (container_)
+    container_->RemoveObserver(this);
+}
+
+aura::Window::Windows MruWindowTracker::GetWindowList() const {
+  return aura::Window::Windows(mru_windows_.begin(), mru_windows_.end());
+}
+
+void MruWindowTracker::MoveToFront(aura::Window* window) {
+  DCHECK(window);
+  CHECK_EQ(container_, window->parent());
+  std::list<aura::Window*>::iterator it =
+      std::find(mru_windows_.begin(), mru_windows_.end(), window);
+  DCHECK(it != mru_windows_.end());
+  mru_windows_.erase(it);
+  mru_windows_.push_back(window);
+}
+
+// Overridden from WindowObserver:
+void MruWindowTracker::OnWillRemoveWindow(aura::Window* window) {
+  std::list<aura::Window*>::iterator it =
+      std::find(mru_windows_.begin(), mru_windows_.end(), window);
+  if (it == mru_windows_.end()) {
+    // All normal windows should be tracked in mru_windows_
+    DCHECK_NE(window->type(), ui::wm::WINDOW_TYPE_NORMAL);
+    return;
+  }
+  mru_windows_.erase(it);
+}
+
+void MruWindowTracker::OnWindowAdded(aura::Window* new_window) {
+  // We are only interested in ordering normal windows.
+  if (new_window->type() == ui::wm::WINDOW_TYPE_NORMAL)
+    mru_windows_.push_back(new_window);
+}
+
+}  // namespace athena
diff --git a/athena/wm/mru_window_tracker.h b/athena/wm/mru_window_tracker.h
new file mode 100644
index 0000000..0ec9d98
--- /dev/null
+++ b/athena/wm/mru_window_tracker.h
@@ -0,0 +1,49 @@
+// Copyright 2014 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 ATHENA_WM_MRU_WINDOW_TRACKER_H_
+#define ATHENA_WM_MRU_WINDOW_TRACKER_H_
+
+#include <list>
+
+#include "athena/wm/public/window_list_provider.h"
+#include "ui/aura/window_observer.h"
+
+namespace aura {
+class Window;
+}
+
+namespace athena {
+
+// Maintains a most recently used list of windows. This is used for window
+// cycling and overview mode.
+class MruWindowTracker : public WindowListProvider,
+                         public aura::WindowObserver {
+ public:
+  explicit MruWindowTracker(aura::Window* container);
+  virtual ~MruWindowTracker();
+
+  // Overridden from WindowListProvider
+  virtual aura::Window::Windows GetWindowList() const OVERRIDE;
+
+  // Updates the mru_windows_ list to move |window| to the front.
+  // |window| must be the child of |container_|.
+  virtual void MoveToFront(aura::Window* window) OVERRIDE;
+
+ private:
+  // Overridden from WindowObserver:
+  virtual void OnWillRemoveWindow(aura::Window* window) OVERRIDE;
+  virtual void OnWindowAdded(aura::Window* new_window) OVERRIDE;
+
+  // List of windows that have been used in the container, sorted by most
+  // recently used.
+  std::list<aura::Window*> mru_windows_;
+  aura::Window* container_;
+
+  DISALLOW_COPY_AND_ASSIGN(MruWindowTracker);
+};
+
+}  // namespace athena
+
+#endif  // ATHENA_WM_MRU_WINDOW_TRACKER_H_
diff --git a/athena/wm/public/window_list_provider.h b/athena/wm/public/window_list_provider.h
new file mode 100644
index 0000000..7ffadf4
--- /dev/null
+++ b/athena/wm/public/window_list_provider.h
@@ -0,0 +1,27 @@
+// Copyright 2014 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 ATHENA_WM_PUBLIC_WINDOW_LIST_PROVIDER_H_
+#define ATHENA_WM_PUBLIC_WINDOW_LIST_PROVIDER_H_
+
+#include "athena/athena_export.h"
+#include "ui/aura/window.h"
+
+namespace athena {
+
+// Interface for an ordered list of aura::Window objects.
+class ATHENA_EXPORT WindowListProvider {
+ public:
+  virtual ~WindowListProvider() {}
+
+  // Returns an ordered list of windows.
+  virtual aura::Window::Windows GetWindowList() const = 0;
+
+  // Moves the window to the front of the list.
+  virtual void MoveToFront(aura::Window* window) = 0;
+};
+
+}  // namespace athena
+
+#endif  // ATHENA_WM_PUBLIC_WINDOW_LIST_PROVIDER_H_
diff --git a/athena/wm/public/window_manager.h b/athena/wm/public/window_manager.h
index 23aab7f..04e2cce 100644
--- a/athena/wm/public/window_manager.h
+++ b/athena/wm/public/window_manager.h
@@ -24,6 +24,8 @@ class ATHENA_EXPORT WindowManager {
 
   virtual void ToggleOverview() = 0;
 
+  virtual bool IsOverviewModeActive() = 0;
+
   virtual void AddObserver(WindowManagerObserver* observer) = 0;
   virtual void RemoveObserver(WindowManagerObserver* observer) = 0;
 };
diff --git a/athena/wm/public/window_manager_observer.h b/athena/wm/public/window_manager_observer.h
index e7f6bcf..216b58c 100644
--- a/athena/wm/public/window_manager_observer.h
+++ b/athena/wm/public/window_manager_observer.h
@@ -13,10 +13,10 @@ class ATHENA_EXPORT WindowManagerObserver {
  public:
   virtual ~WindowManagerObserver() {}
 
-  // Called when the overview mode is displayed.
+  // Called immediately before the overview mode is displayed.
   virtual void OnOverviewModeEnter() = 0;
 
-  // Called when going out of overview mode.
+  // Called immediately after going out of the overview mode.
   virtual void OnOverviewModeExit() = 0;
 };
 
diff --git a/athena/wm/split_view_controller.cc b/athena/wm/split_view_controller.cc
index 7da3675..595a61a 100644
--- a/athena/wm/split_view_controller.cc
+++ b/athena/wm/split_view_controller.cc
@@ -4,29 +4,273 @@
 
 #include "athena/wm/split_view_controller.h"
 
+#include <cmath>
+
+#include "athena/wm/public/window_list_provider.h"
+#include "athena/wm/public/window_manager.h"
+#include "base/bind.h"
 #include "ui/aura/window.h"
+#include "ui/compositor/layer_animation_observer.h"
+#include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/events/event_handler.h"
+#include "ui/gfx/display.h"
+#include "ui/gfx/screen.h"
 
 namespace athena {
+namespace {
+
+// An animation observer that runs a callback at the end of the animation, and
+// destroys itself.
+class CallbackAnimationObserver : public ui::ImplicitAnimationObserver {
+ public:
+  explicit CallbackAnimationObserver(const base::Closure& closure)
+      : closure_(closure) {}
+
+  virtual ~CallbackAnimationObserver() {}
+
+ private:
+  // Overridden from ui::ImplicitAnimationObserver:
+  virtual void OnImplicitAnimationsCompleted() OVERRIDE {
+    if (!closure_.is_null())
+      closure_.Run();
+    delete this;
+  }
 
-SplitViewController::SplitViewController() {
+  const base::Closure closure_;
+
+  DISALLOW_COPY_AND_ASSIGN(CallbackAnimationObserver);
+};
+
+}  // namespace
+
+SplitViewController::SplitViewController(
+    aura::Window* container,
+    WindowListProvider* window_list_provider,
+    WindowManager* window_manager)
+    : state_(INACTIVE),
+      container_(container),
+      window_manager_(window_manager),
+      window_list_provider_(window_list_provider),
+      current_activity_window_(NULL),
+      left_window_(NULL),
+      right_window_(NULL),
+      separator_position_(0),
+      weak_factory_(this) {
+  window_manager->AddObserver(this);
 }
 
 SplitViewController::~SplitViewController() {
+  window_manager_->RemoveObserver(this);
+}
+
+bool SplitViewController::IsSplitViewModeActive() const {
+  return state_ == ACTIVE;
+}
+
+void SplitViewController::UpdateLayout(bool animate) {
+  if  (!left_window_)
+    return;
+  CHECK(right_window_);
+  gfx::Transform left_transform;
+  gfx::Transform right_transform;
+  int container_width = container_->GetBoundsInScreen().width();
+  if (state_ == ACTIVE) {
+    // This method should only be called once in ACTIVE state when
+    // the left and rightwindows are still full screen and need to be resized.
+    CHECK_EQ(left_window_->bounds().width(), container_width);
+    CHECK_EQ(right_window_->bounds().width(), container_width);
+    // Windows should be resized via an animation when entering the ACTIVE
+    // state.
+    CHECK(animate);
+    // We scale the windows here, but when the animation finishes, we reset
+    // the scaling and update the window bounds to the proper size - see
+    // OnAnimationCompleted().
+    left_transform.Scale(.5, 1);
+    right_transform.Scale(.5, 1);
+    right_transform.Translate(container_width, 0);
+  } else {
+    left_transform.Translate(separator_position_ - container_width, 0);
+    right_transform.Translate(separator_position_, 0);
+  }
+  left_window_->Show();
+  right_window_->Show();
+  SetWindowTransform(left_window_, left_transform, animate);
+  SetWindowTransform(right_window_, right_transform, animate);
+}
+
+void SplitViewController::SetWindowTransform(aura::Window* window,
+                                             const gfx::Transform& transform,
+                                             bool animate) {
+  if (animate) {
+    scoped_refptr<ui::LayerAnimator> animator = window->layer()->GetAnimator();
+    ui::ScopedLayerAnimationSettings settings(animator);
+    settings.SetPreemptionStrategy(
+        ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+    settings.AddObserver(new CallbackAnimationObserver(
+        base::Bind(&SplitViewController::OnAnimationCompleted,
+                   weak_factory_.GetWeakPtr(),
+                   window)));
+    window->SetTransform(transform);
+  } else {
+    window->SetTransform(transform);
+  }
+}
+
+void SplitViewController::OnAnimationCompleted(aura::Window* window) {
+  DCHECK(window == left_window_ || window == right_window_);
+  if (state_ == ACTIVE) {
+    gfx::Rect window_bounds = gfx::Rect(container_->bounds().size());
+    int container_width = window_bounds.width();
+    window_bounds.set_width(container_width / 2);
+    window->SetTransform(gfx::Transform());
+    if (window == left_window_) {
+      left_window_->SetBounds(window_bounds);
+    } else {
+      window_bounds.set_x(container_width / 2);
+      right_window_->SetBounds(window_bounds);
+    }
+  } else {
+    int container_width = container_->bounds().width();
+    window->SetTransform(gfx::Transform());
+    if (window == left_window_) {
+      if (separator_position_ == 0)
+        left_window_->Hide();
+      if (state_ == INACTIVE)
+        left_window_ = NULL;
+    } else {
+      if (separator_position_ == container_width)
+        right_window_->Hide();
+      if (state_ == INACTIVE)
+        right_window_ = NULL;
+    }
+  }
 }
 
+void SplitViewController::UpdateSeparatorPositionFromScrollDelta(float delta) {
+  gfx::Screen* screen = gfx::Screen::GetScreenFor(container_);
+  const gfx::Rect& display_bounds =
+      screen->GetDisplayNearestWindow(container_).bounds();
+  gfx::Rect container_bounds = container_->GetBoundsInScreen();
+  separator_position_ =
+      delta > 0 ? ((int)delta) + display_bounds.x() - container_bounds.x()
+                : display_bounds.right() - container_bounds.x() + delta;
+}
+
+aura::Window* SplitViewController::GetCurrentActivityWindow() {
+  if (!current_activity_window_) {
+    aura::Window::Windows windows = window_list_provider_->GetWindowList();
+    if (windows.empty())
+      return NULL;
+    current_activity_window_ = windows.back();
+  }
+  return current_activity_window_;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Begin BezelController::ScrollDelegate overrides.
 void SplitViewController::ScrollBegin(BezelController::Bezel bezel,
                                       float delta) {
+  if (!CanScroll())
+    return;
+  state_ = SCROLLING;
+  aura::Window* current_window = GetCurrentActivityWindow();
+  CHECK(current_window);
+
+  aura::Window::Windows windows = window_list_provider_->GetWindowList();
+  CHECK(windows.size() >= 2);
+  aura::Window::Windows::const_iterator it =
+      std::find(windows.begin(), windows.end(), current_window);
+  CHECK(it != windows.end());
+
+  if (delta > 0) {
+    right_window_ = current_window;
+    // reverse iterator points to the position before normal iterator |it|
+    aura::Window::Windows::const_reverse_iterator rev_it(it);
+    // circle to end if needed.
+    left_window_ = rev_it == windows.rend() ? windows.back() : *(rev_it);
+  } else {
+    left_window_ = current_window;
+    ++it;
+    // circle to front if needed.
+    right_window_ = it == windows.end() ? windows.front() : *it;
+  }
+
+  CHECK(left_window_);
+  CHECK(right_window_);
+
+  // TODO(oshima|mfomitchev): crbug.com/388362
+  // Until we are properly hiding off-screen windows in window manager:
+  // Loop through all windows and hide them
+  for (it = windows.begin(); it != windows.end(); ++it) {
+    if (*it != left_window_ && *it != right_window_)
+      (*it)->Hide();
+  }
+
+  UpdateSeparatorPositionFromScrollDelta(delta);
+  UpdateLayout(false);
 }
 
+// Max distance from the scroll end position to the middle of the screen where
+// we would go into the split view mode.
+const int kMaxDistanceFromMiddle = 120;
 void SplitViewController::ScrollEnd() {
+  if (state_ != SCROLLING)
+    return;
+
+  int container_width = container_->GetBoundsInScreen().width();
+  if (std::abs(container_width / 2 - separator_position_) <=
+      kMaxDistanceFromMiddle) {
+    state_ = ACTIVE;
+    separator_position_ = container_width / 2;
+  } else if (separator_position_ < container_width / 2) {
+    separator_position_ = 0;
+    current_activity_window_ = right_window_;
+    state_ = INACTIVE;
+  } else {
+    separator_position_ = container_width;
+    current_activity_window_ = left_window_;
+    state_ = INACTIVE;
+  }
+  UpdateLayout(true);
 }
 
 void SplitViewController::ScrollUpdate(float delta) {
+  if (state_ != SCROLLING)
+    return;
+  UpdateSeparatorPositionFromScrollDelta(delta);
+  UpdateLayout(false);
 }
 
 bool SplitViewController::CanScroll() {
-  return false;
+  // TODO(mfomitchev): return false in vertical orientation, in full screen.
+  bool result = (!window_manager_->IsOverviewModeActive() &&
+                 !IsSplitViewModeActive() &&
+                 window_list_provider_->GetWindowList().size() >= 2);
+  return result;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// WindowManagerObserver overrides
+void SplitViewController::OnOverviewModeEnter() {
+  if (state_ == ACTIVE) {
+    CHECK(left_window_);
+    CHECK(right_window_);
+    window_list_provider_->MoveToFront(right_window_);
+    window_list_provider_->MoveToFront(left_window_);
+    // TODO(mfomitchev): This shouldn't be done here, but the overview mode's
+    // transition animation currently looks bad if the starting transform of
+    // any window is not gfx::Transform().
+    right_window_->SetTransform(gfx::Transform());
+  } else if (current_activity_window_) {
+    window_list_provider_->MoveToFront(current_activity_window_);
+  }
+  state_ = INACTIVE;
+  left_window_ = NULL;
+  right_window_ = NULL;
+  current_activity_window_ = NULL;
+}
+
+void SplitViewController::OnOverviewModeExit() {
 }
 
 }  // namespace athena
diff --git a/athena/wm/split_view_controller.h b/athena/wm/split_view_controller.h
index e0652de..337b75b 100644
--- a/athena/wm/split_view_controller.h
+++ b/athena/wm/split_view_controller.h
@@ -6,24 +6,99 @@
 #define ATHENA_WM_SPLIT_VIEW_CONTROLLER_H_
 
 #include "athena/wm/bezel_controller.h"
+#include "athena/wm/public/window_manager_observer.h"
+#include "athena/wm/window_overview_mode.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+
+namespace gfx {
+class Transform;
+}
 
 namespace athena {
+class WindowListProvider;
+class WindowManager;
+class WindowOverviewModeDelegate;
 
 // Responsible for entering split view mode, exiting from split view mode, and
 // laying out the windows in split view mode.
-class SplitViewController : public BezelController::ScrollDelegate {
+class SplitViewController : public BezelController::ScrollDelegate,
+                            public WindowManagerObserver {
  public:
-  SplitViewController();
+  SplitViewController(aura::Window* container,
+                      WindowListProvider* window_list_provider,
+                      WindowManager* window_manager);
+
   virtual ~SplitViewController();
 
+  bool IsSplitViewModeActive() const;
+
  private:
+  enum State {
+    // Split View mode is not active. |left_window_| and |right_window| are
+    // NULL.
+    INACTIVE,
+    // Two windows |left_window_| and |right_window| are shown side by side and
+    // there is a horizontal scroll in progress which is dragging the separator
+    // between the two windows.
+    SCROLLING,
+    // Split View mode is active with |left_window_| and |right_window| showing
+    // side by side each occupying half the screen. No scroll in progress.
+    ACTIVE
+  };
+
+  void UpdateLayout(bool animate);
+
+  void SetWindowTransform(aura::Window* left_window,
+                          const gfx::Transform& transform,
+                          bool animate);
+
+  void OnAnimationCompleted(aura::Window* window);
+
+  void UpdateSeparatorPositionFromScrollDelta(float delta);
+
+  // Returns the current activity shown to the user. Persists through the
+  // SCROLLING and ACTIVE states and gets updated if the current activity goes
+  // off screen when the user switches between activities.
+  aura::Window* GetCurrentActivityWindow();
+
   // BezelController::ScrollDelegate overrides.
   virtual void ScrollBegin(BezelController::Bezel bezel, float delta) OVERRIDE;
   virtual void ScrollEnd() OVERRIDE;
   virtual void ScrollUpdate(float delta) OVERRIDE;
   virtual bool CanScroll() OVERRIDE;
 
+  // WindowManagerObserver
+  virtual void OnOverviewModeEnter() OVERRIDE;
+  virtual void OnOverviewModeExit() OVERRIDE;
+
+  State state_;
+
+  aura::Window* container_;
+
+  // Window Manager which owns this SplitViewController.
+  // Must be non NULL for the duration of the lifetime.
+  WindowManager* window_manager_;
+
+  // Provider of the list of windows to cycle through. Not owned.
+  WindowListProvider* window_list_provider_;
+
+  // Keeps track of the current activity shown as the user switches between
+  // activities. Persists through the SCROLLING and ACTIVE states. Gets reset
+  // to NULL when overview mode is activated.
+  aura::Window* current_activity_window_;
+
+  // Windows for the left and right activities shown in SCROLLING and ACTIVE
+  // states. In INACTIVE state these are NULL.
+  aura::Window* left_window_;
+  aura::Window* right_window_;
+
+  // Position of the separator between left_window_ and right_window_ in
+  // container_ coordinates (along the x axis).
+  int separator_position_;
+
+  base::WeakPtrFactory<SplitViewController> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(SplitViewController);
 };
 
diff --git a/athena/wm/window_manager_impl.cc b/athena/wm/window_manager_impl.cc
index 560252a..37daf43 100644
--- a/athena/wm/window_manager_impl.cc
+++ b/athena/wm/window_manager_impl.cc
@@ -10,6 +10,7 @@
 #include "athena/input/public/accelerator_manager.h"
 #include "athena/screen/public/screen_manager.h"
 #include "athena/wm/bezel_controller.h"
+#include "athena/wm/mru_window_tracker.h"
 #include "athena/wm/public/window_manager_observer.h"
 #include "athena/wm/split_view_controller.h"
 #include "athena/wm/title_drag_controller.h"
@@ -41,6 +42,8 @@ class WindowManagerImpl : public WindowManager,
   // WindowManager:
   virtual void ToggleOverview() OVERRIDE;
 
+  virtual bool IsOverviewModeActive() OVERRIDE;
+
  private:
   enum Command {
     CMD_TOGGLE_OVERVIEW,
@@ -74,6 +77,7 @@ class WindowManagerImpl : public WindowManager,
   virtual void OnTitleDragCanceled(aura::Window* window) OVERRIDE;
 
   scoped_ptr<aura::Window> container_;
+  scoped_ptr<MruWindowTracker> mru_window_tracker_;
   scoped_ptr<WindowOverviewMode> overview_;
   scoped_ptr<BezelController> bezel_controller_;
   scoped_ptr<SplitViewController> split_view_controller_;
@@ -112,8 +116,10 @@ WindowManagerImpl::WindowManagerImpl() {
   container_.reset(ScreenManager::Get()->CreateDefaultContainer(params));
   container_->SetLayoutManager(new AthenaContainerLayoutManager);
   container_->AddObserver(this);
+  mru_window_tracker_.reset(new MruWindowTracker(container_.get()));
   bezel_controller_.reset(new BezelController(container_.get()));
-  split_view_controller_.reset(new SplitViewController());
+  split_view_controller_.reset(new SplitViewController(
+      container_.get(), mru_window_tracker_.get(), this));
   bezel_controller_->set_left_right_delegate(split_view_controller_.get());
   container_->AddPreTargetHandler(bezel_controller_.get());
   title_drag_controller_.reset(new TitleDragController(container_.get(), this));
@@ -127,6 +133,7 @@ WindowManagerImpl::WindowManagerImpl() {
 
 WindowManagerImpl::~WindowManagerImpl() {
   overview_.reset();
+  mru_window_tracker_.reset();
   if (container_) {
     container_->RemoveObserver(this);
     container_->RemovePreTargetHandler(bezel_controller_.get());
@@ -154,15 +161,26 @@ void WindowManagerImpl::ToggleOverview() {
   SetInOverview(overview_.get() == NULL);
 }
 
+bool WindowManagerImpl::IsOverviewModeActive() {
+  return overview_;
+}
+
 void WindowManagerImpl::SetInOverview(bool active) {
   bool in_overview = !!overview_;
   if (active == in_overview)
     return;
 
   if (active) {
-    overview_ = WindowOverviewMode::Create(container_.get(), this);
     FOR_EACH_OBSERVER(WindowManagerObserver, observers_,
                       OnOverviewModeEnter());
+    // Re-stack all windows in the order defined by mru_window_tracker_.
+    aura::Window::Windows window_list = mru_window_tracker_->GetWindowList();
+    aura::Window::Windows::iterator it;
+    for (it = window_list.begin(); it != window_list.end(); ++it)
+      container_->StackChildAtTop(*it);
+    overview_ = WindowOverviewMode::Create(container_.get(),
+                                           mru_window_tracker_.get(),
+                                           this);
   } else {
     overview_.reset();
     FOR_EACH_OBSERVER(WindowManagerObserver, observers_,
@@ -188,8 +206,7 @@ void WindowManagerImpl::RemoveObserver(WindowManagerObserver* observer) {
 }
 
 void WindowManagerImpl::OnSelectWindow(aura::Window* window) {
-  CHECK_EQ(container_.get(), window->parent());
-  container_->StackChildAtTop(window);
+  mru_window_tracker_->MoveToFront(window);
   wm::ActivateWindow(window);
   SetInOverview(false);
 }
diff --git a/athena/wm/window_overview_mode.cc b/athena/wm/window_overview_mode.cc
index efad0b1..91ee8c9 100644
--- a/athena/wm/window_overview_mode.cc
+++ b/athena/wm/window_overview_mode.cc
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "athena/common/closure_animation_observer.h"
+#include "athena/wm/public/window_list_provider.h"
 #include "base/bind.h"
 #include "base/macros.h"
 #include "ui/aura/scoped_window_targeter.h"
@@ -50,10 +51,6 @@ namespace athena {
 
 namespace {
 
-bool ShouldShowWindowInOverviewMode(aura::Window* window) {
-  return window->type() == ui::wm::WINDOW_TYPE_NORMAL;
-}
-
 // Gets the transform for the window in its current state.
 gfx::Transform GetTransformForState(WindowOverviewState* state) {
   return gfx::Tween::TransformValueBetween(state->progress,
@@ -108,8 +105,10 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
                                public ui::CompositorAnimationObserver {
  public:
   WindowOverviewModeImpl(aura::Window* container,
+                         const WindowListProvider* window_list_provider,
                          WindowOverviewModeDelegate* delegate)
       : container_(container),
+        window_list_provider_(window_list_provider),
         delegate_(delegate),
         scoped_targeter_(new aura::ScopedWindowTargeter(
             container,
@@ -127,13 +126,10 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
   virtual ~WindowOverviewModeImpl() {
     container_->set_target_handler(container_->delegate());
     RemoveAnimationObserver();
-    const aura::Window::Windows& windows = container_->children();
-    for (aura::Window::Windows::const_iterator iter = windows.begin();
-         iter != windows.end();
-         ++iter) {
-      if ((*iter)->GetProperty(kWindowOverviewState))
-        RestoreWindowState(*iter);
-    }
+    aura::Window::Windows windows = window_list_provider_->GetWindowList();
+    if (windows.empty())
+      return;
+    std::for_each(windows.begin(), windows.end(), &RestoreWindowState);
   }
 
  private:
@@ -141,10 +137,8 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
   // positions. The transforms are set in the |kWindowOverviewState| property of
   // the windows.
   void ComputeTerminalStatesForAllWindows() {
-    const aura::Window::Windows& windows = container_->children();
-    size_t window_count = std::count_if(windows.begin(), windows.end(),
-                                        ShouldShowWindowInOverviewMode);
-
+    aura::Window::Windows windows = window_list_provider_->GetWindowList();
+    size_t window_count = windows.size();
     size_t index = 0;
     const gfx::Size container_size = container_->bounds().size();
 
@@ -153,10 +147,8 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
 
     for (aura::Window::Windows::const_reverse_iterator iter = windows.rbegin();
          iter != windows.rend();
-         ++iter) {
+         ++iter, ++index) {
       aura::Window* window = (*iter);
-      if (!ShouldShowWindowInOverviewMode(window))
-        continue;
 
       gfx::Transform top_transform;
       int top = (window_count - index - 1) * kGapBetweenWindowsTop;
@@ -176,27 +168,20 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
       state->progress = 0.f;
       window->SetProperty(kWindowOverviewState, state);
       wm::SetShadowType(window, wm::SHADOW_TYPE_RECTANGULAR_ALWAYS_ACTIVE);
-
-      index++;
     }
   }
 
   // Sets the initial position for the windows for the overview mode.
   void SetInitialWindowStates() {
+    aura::Window::Windows windows = window_list_provider_->GetWindowList();
+    size_t window_count = windows.size();
     // The initial overview state of the topmost three windows.
     const float kInitialProgress[] = { 0.5f, 0.05f, 0.01f };
-    size_t index = 0;
-    const aura::Window::Windows& windows = container_->children();
-    for (aura::Window::Windows::const_reverse_iterator iter = windows.rbegin();
-         iter != windows.rend();
-         ++iter) {
-      aura::Window* window = (*iter);
-      if (!window->GetProperty(kWindowOverviewState))
-        continue;
-
+    for (size_t i = 0; i < window_count; ++i) {
       float progress = 0.f;
-      if (index < arraysize(kInitialProgress))
-        progress = kInitialProgress[index];
+      aura::Window* window = windows[window_count - 1 - i];
+      if (i < arraysize(kInitialProgress))
+        progress = kInitialProgress[i];
 
       scoped_refptr<ui::LayerAnimator> animator =
           window->layer()->GetAnimator();
@@ -217,7 +202,6 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
         settings.SetTransitionDuration(base::TimeDelta::FromMilliseconds(250));
         SetWindowProgress(window, progress);
       }
-      index++;
     }
   }
 
@@ -244,7 +228,7 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
   void DoScroll(float delta_y) {
     const float kEpsilon = 1e-3f;
     float delta_y_p = std::abs(delta_y) / GetScrollableHeight();
-    const aura::Window::Windows& windows = container_->children();
+    aura::Window::Windows windows = window_list_provider_->GetWindowList();
     if (delta_y < 0) {
       // Scroll up. Start with the top-most (i.e. behind-most in terms of
       // z-index) window, and try to scroll them up.
@@ -253,8 +237,6 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
            ++iter) {
         aura::Window* window = (*iter);
         WindowOverviewState* state = window->GetProperty(kWindowOverviewState);
-        if (!state)
-          continue;
         if (state->progress > kEpsilon) {
           // It is possible to scroll |window| up. Scroll it up, and update
           // |delta_y_p| for the next window.
@@ -266,14 +248,12 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
     } else {
       // Scroll down. Start with the bottom-most (i.e. front-most in terms of
       // z-index) window, and try to scroll them down.
-      for (aura::Window::Windows::const_reverse_iterator iter =
-               windows.rbegin();
+      aura::Window::Windows::const_reverse_iterator iter;
+      for (iter = windows.rbegin();
            delta_y_p > kEpsilon && iter != windows.rend();
            ++iter) {
         aura::Window* window = (*iter);
         WindowOverviewState* state = window->GetProperty(kWindowOverviewState);
-        if (!state)
-          continue;
         if (1.f - state->progress > kEpsilon) {
           // It is possible to scroll |window| down. Scroll it down, and update
           // |delta_y_p| for the next window.
@@ -489,6 +469,8 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
   const float kMinOpacity = 0.2f;
 
   aura::Window* container_;
+  // Provider of the stack of windows to show in the overview mode. Not owned.
+  const WindowListProvider* window_list_provider_;
   WindowOverviewModeDelegate* delegate_;
   scoped_ptr<aura::ScopedWindowTargeter> scoped_targeter_;
   scoped_ptr<ui::FlingCurve> fling_;
@@ -504,9 +486,10 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
 // static
 scoped_ptr<WindowOverviewMode> WindowOverviewMode::Create(
     aura::Window* container,
+    const WindowListProvider* window_list_provider,
     WindowOverviewModeDelegate* delegate) {
   return scoped_ptr<WindowOverviewMode>(
-      new WindowOverviewModeImpl(container, delegate));
+      new WindowOverviewModeImpl(container, window_list_provider, delegate));
 }
 
 }  // namespace athena
diff --git a/athena/wm/window_overview_mode.h b/athena/wm/window_overview_mode.h
index 46eb249..a95a0fb 100644
--- a/athena/wm/window_overview_mode.h
+++ b/athena/wm/window_overview_mode.h
@@ -6,12 +6,10 @@
 #define ATHENA_WM_WINDOW_OVERVIEW_MODE_H_
 
 #include "base/memory/scoped_ptr.h"
-
-namespace aura {
-class Window;
-}
+#include "ui/aura/window.h"
 
 namespace athena {
+class WindowListProvider;
 
 class WindowOverviewModeDelegate {
  public:
@@ -26,6 +24,7 @@ class WindowOverviewMode {
 
   static scoped_ptr<WindowOverviewMode> Create(
       aura::Window* container,
+      const WindowListProvider* window_list_provider,
       WindowOverviewModeDelegate* delegate);
 };