Fixes bug in WmWindowAura::OnWindowVisibilityChanged()

The code was assuming window was this->window_, which is not
necessarily the case.

BUG=650755
TEST=none
R=oshima@chromium.org

Review-Url: https://codereview.chromium.org/2369413002
Cr-Commit-Position: refs/heads/master@{#421298}

ash/aura/wm_window_aura.cc

@@ -857,6 +857,7 @@ void WmWindowAura::OnWindowDestroyed(aura::Window* window) {
 
 void WmWindowAura::OnWindowVisibilityChanging(aura::Window* window,
                                               bool visible) {
+  DCHECK_EQ(window, window_);
   FOR_EACH_OBSERVER(WmWindowObserver, observers_,
                     OnWindowVisibilityChanging(this, visible));
 }
@@ -864,7 +865,7 @@ void WmWindowAura::OnWindowVisibilityChanging(aura::Window* window,
 void WmWindowAura::OnWindowVisibilityChanged(aura::Window* window,
                                              bool visible) {
   FOR_EACH_OBSERVER(WmWindowObserver, observers_,
-                    OnWindowVisibilityChanged(this, visible));
+                    OnWindowVisibilityChanged(Get(window), visible));
 }
 
 void WmWindowAura::OnWindowTitleChanged(aura::Window* window) {

ui/aura/window_observer.h

@@ -70,6 +70,12 @@ class AURA_EXPORT WindowObserver {
   // value supplied to SetVisible(). If |visible| is true, window->IsVisible()
   // may still return false. See description in Window::IsVisible() for details.
   virtual void OnWindowVisibilityChanging(Window* window, bool visible) {}
+
+  // When the visibility of a Window changes OnWindowVisibilityChanged() is
+  // called for all observers attached to descendants of the Window as well
+  // as all observers attached to ancestors of the Window. The Window supplied
+  // to OnWindowVisibilityChanged() is the Window that Show()/Hide() was called
+  // on.
   virtual void OnWindowVisibilityChanged(Window* window, bool visible) {}
 
   // Invoked when SetBounds() is invoked on |window|. |old_bounds| and