Keep the split view activities topmost in z-order in Athena

athena/wm/split_view_controller.cc

Index: athena/wm/split_view_controller.cc
diff --git a/athena/wm/split_view_controller.cc b/athena/wm/split_view_controller.cc
index 85db209536916f46ec72f8d59b586abf056f9e4e..e9485c1887b751c6ca10a7ca4528e6ec8f2d9aee 100644
--- a/athena/wm/split_view_controller.cc
+++ b/athena/wm/split_view_controller.cc
@@ -62,6 +62,9 @@ bool SplitViewController::IsSplitViewModeActive() const {
 
 void SplitViewController::ActivateSplitMode(aura::Window* left,
                                             aura::Window* right) {
+  DCHECK((left && wm::IsActiveWindow(left)) ||
+         (right && wm::IsActiveWindow(right)));
+
   aura::Window::Windows windows = window_list_provider_->GetWindowList();
   aura::Window::Windows::reverse_iterator iter = windows.rbegin();
   if (state_ == ACTIVE) {
@@ -95,14 +98,8 @@ void SplitViewController::ActivateSplitMode(aura::Window* left,
   }
 
   SetState(ACTIVE);
-  if (right_window_ != right) {
-    right_window_ = right;
-    container_->StackChildAtTop(right_window_);
-  }
-  if (left_window_ != left) {
-    left_window_ = left;
-    container_->StackChildAtTop(left_window_);
-  }
+  right_window_ = right;
+  left_window_ = left;
   UpdateLayout(true);
 }
 
@@ -122,7 +119,6 @@ void SplitViewController::ReplaceWindow(aura::Window* window,
     left_window_ = replace_with;
   else
     right_window_ = replace_with;
-  wm::ActivateWindow(replace_with);
   UpdateLayout(false);
   window->SetTransform(gfx::Transform());
   window->Hide();
@@ -175,6 +171,12 @@ void SplitViewController::UpdateLayout(bool animate) {
 
   left_window_->Show();
   right_window_->Show();
+  DCHECK(wm::IsActiveWindow(left_window_) || wm::IsActiveWindow(right_window_));
+  if (wm::IsActiveWindow(left_window_))
+    container_->StackChildBelow(right_window_, left_window_);
+  if (wm::IsActiveWindow(right_window_))
+    container_->StackChildBelow(left_window_, right_window_);
+
   if (state_ == ACTIVE) {
     if (animate) {
       gfx::Transform left_transform = GetTargetTransformForBoundsAnimation(