athena: Add a test for split-view controller.

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 cde465798a80420057ab96ae344b69ef951a8cad..35a43ea0ded2bf7c40f74297701628bd95190a89 100644
--- a/athena/wm/split_view_controller.cc
+++ b/athena/wm/split_view_controller.cc
@@ -56,11 +56,13 @@ SplitViewController::SplitViewController(
       right_window_(NULL),
       separator_position_(0),
       weak_factory_(this) {
-  window_manager->AddObserver(this);
+  if (window_manager_)
+    window_manager_->AddObserver(this);
 }
 
 SplitViewController::~SplitViewController() {
-  window_manager_->RemoveObserver(this);
+  if (window_manager_)
+    window_manager_->RemoveObserver(this);
 }
 
 bool SplitViewController::IsSplitViewModeActive() const {
@@ -72,6 +74,11 @@ void SplitViewController::ActivateSplitMode(aura::Window* left,
   aura::Window::Windows windows = window_list_provider_->GetWindowList();
   aura::Window::Windows::reverse_iterator iter = windows.rbegin();
   if (state_ == ACTIVE) {
+    if (left_window_ == right)
+      left_window_ = left;
+    if (right_window_ == left)
+      right_window_ = right;
+
     if (!left)
       left = left_window_;
     if (!right)
@@ -280,7 +287,7 @@ void SplitViewController::ScrollUpdate(float delta) {
 
 bool SplitViewController::CanScroll() {
   // TODO(mfomitchev): return false in vertical orientation, in full screen.
-  bool result = (!window_manager_->IsOverviewModeActive() &&
+  bool result = (window_manager_ && !window_manager_->IsOverviewModeActive() &&
                  !IsSplitViewModeActive() &&
                  window_list_provider_->GetWindowList().size() >= 2);
   return result;