athena: Move windows in the stack backwards if the back-most window is closed.

When in overview mode, if a window is closed, then the rest of the windows
that behind the closed window in the stack are moved on step forward. However,
if there are no windows behind the closed window, then move the windows in
front of the closed window backward one step.

BUG=408280
R=oshima@chromium.org

Review URL: https://codereview.chromium.org/531093003

Cr-Commit-Position: refs/heads/master@{#293196}

athena/wm/window_overview_mode.cc

@@ -189,6 +189,10 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
     }
   }
 
+  // Computes the terminal states (i.e. the transforms for the top-most and
+  // bottom-most position in the stack) for |window|. |window_count| is the
+  // number of windows in the stack, and |index| is the position of the window
+  // in the stack (0 being the front-most window).
   void UpdateTerminalStateForWindowAtIndex(aura::Window* window,
                                            size_t index,
                                            size_t window_count) {
@@ -418,45 +422,72 @@ class WindowOverviewModeImpl : public WindowOverviewMode,
 
   void CloseDragWindow(const ui::GestureEvent& gesture) {
     // Animate |dragged_window_| offscreen first, then destroy it.
-    ui::ScopedLayerAnimationSettings settings(
-        dragged_window_->layer()->GetAnimator());
-    settings.SetPreemptionStrategy(
-        ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
-    settings.AddObserver(new ui::ClosureAnimationObserver(
-        base::Bind(&base::DeletePointer<aura::Window>, dragged_window_)));
-
-    WindowOverviewState* dragged_state =
-        dragged_window_->GetProperty(kWindowOverviewState);
-    CHECK(dragged_state);
-    gfx::Transform transform = dragged_window_->layer()->transform();
-    gfx::RectF transformed_bounds = dragged_window_->bounds();
-    transform.TransformRect(&transformed_bounds);
-    float transform_x = 0.f;
-    if (gesture.location().x() > dragged_start_location_.x())
-      transform_x = container_->bounds().right() - transformed_bounds.x();
-    else
-      transform_x = -(transformed_bounds.x() + transformed_bounds.width());
-    float scale = gfx::Tween::FloatValueBetween(
-        dragged_state->progress, kMinScale, kMaxScale);
-    transform.Translate(transform_x / scale, 0);
-    dragged_window_->SetTransform(transform);
-    dragged_window_->layer()->SetOpacity(kMinOpacity);
-
-    // Move the windows behind |dragged_window_| in the stack forward one step.
-    const aura::Window::Windows& list = container_->children();
-    for (aura::Window::Windows::const_iterator iter = list.begin();
-         iter != list.end() && *iter != dragged_window_;
-         ++iter) {
-      aura::Window* window = *iter;
-      ui::ScopedLayerAnimationSettings settings(window->layer()->GetAnimator());
+    {
+      ui::ScopedLayerAnimationSettings settings(
+          dragged_window_->layer()->GetAnimator());
       settings.SetPreemptionStrategy(
           ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+      settings.AddObserver(new ui::ClosureAnimationObserver(
+          base::Bind(&base::DeletePointer<aura::Window>, dragged_window_)));
+
+      WindowOverviewState* dragged_state =
+          dragged_window_->GetProperty(kWindowOverviewState);
+      CHECK(dragged_state);
+      gfx::Transform transform = dragged_window_->layer()->transform();
+      gfx::RectF transformed_bounds = dragged_window_->bounds();
+      transform.TransformRect(&transformed_bounds);
+      float transform_x = 0.f;
+      if (gesture.location().x() > dragged_start_location_.x())
+        transform_x = container_->bounds().right() - transformed_bounds.x();
+      else
+        transform_x = -(transformed_bounds.x() + transformed_bounds.width());
+      float scale = gfx::Tween::FloatValueBetween(
+          dragged_state->progress, kMinScale, kMaxScale);
+      transform.Translate(transform_x / scale, 0);
+      dragged_window_->SetTransform(transform);
+      dragged_window_->layer()->SetOpacity(kMinOpacity);
+    }
+
+    const aura::Window::Windows list = window_list_provider_->GetWindowList();
+    CHECK(!list.empty());
+    if (list.front() == dragged_window_) {
+      // There's no window behind |dragged_window_|. So move the windows in
+      // front take a step back.
+      for (aura::Window::Windows::const_reverse_iterator iter = list.rbegin();
+           iter != list.rend() && *iter != dragged_window_;
+           ++iter) {
+        aura::Window* window = *iter;
+        ui::ScopedLayerAnimationSettings settings(
+            window->layer()->GetAnimator());
+        settings.SetPreemptionStrategy(
+            ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
 
-      aura::Window* next = *(iter + 1);
-      WindowOverviewState* next_state = next->GetProperty(kWindowOverviewState);
-      UpdateTerminalStateForWindowAtIndex(window, list.end() - iter,
-                                          list.size());
-      SetWindowProgress(window, next_state->progress);
+        aura::Window* next = *(iter + 1);
+        WindowOverviewState* next_state =
+            next->GetProperty(kWindowOverviewState);
+        UpdateTerminalStateForWindowAtIndex(
+            window, iter - list.rbegin(), list.size());
+        SetWindowProgress(window, next_state->progress);
+      }
+    } else {
+      // Move the windows behind |dragged_window_| in the stack forward one
+      // step.
+      for (aura::Window::Windows::const_iterator iter = list.begin();
+           iter != list.end() && *iter != dragged_window_;
+           ++iter) {
+        aura::Window* window = *iter;
+        ui::ScopedLayerAnimationSettings settings(
+            window->layer()->GetAnimator());
+        settings.SetPreemptionStrategy(
+            ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+
+        aura::Window* next = *(iter + 1);
+        WindowOverviewState* next_state =
+            next->GetProperty(kWindowOverviewState);
+        UpdateTerminalStateForWindowAtIndex(
+            window, list.end() - iter, list.size());
+        SetWindowProgress(window, next_state->progress);
+      }
     }
 
     dragged_window_ = NULL;