Reland r256396 Add views implementation for AXTreeSource.

chrome/browser/ui/views/panels/panel_view.cc

Index: chrome/browser/ui/views/panels/panel_view.cc
diff --git a/chrome/browser/ui/views/panels/panel_view.cc b/chrome/browser/ui/views/panels/panel_view.cc
index 017cfbebf3e37bff67a7c5ad43c77a9c61dd64b0..e49a0fb6c6cf44292b76a06eac02010a15db8e94 100644
--- a/chrome/browser/ui/views/panels/panel_view.cc
+++ b/chrome/browser/ui/views/panels/panel_view.cc
@@ -311,6 +311,8 @@ PanelView::PanelView(Panel* panel, const gfx::Rect& bounds, bool always_on_top)
 }
 
 PanelView::~PanelView() {
+  if (window_)
+    window_->RemoveObserver(this);
 }
 
 void PanelView::ShowPanel() {
@@ -779,6 +781,7 @@ gfx::ImageSkia PanelView::GetWindowIcon() {
 }
 
 void PanelView::WindowClosing() {
+
   // When closing a panel via window.close, API or the close button,
   // ClosePanel() is called first, destroying the native |window_|
   // which results in this method being called. ClosePanel() sets
@@ -948,7 +951,10 @@ bool PanelView::AcceleratorPressed(const ui::Accelerator& accelerator) {
 }
 
 void PanelView::OnWidgetDestroying(views::Widget* widget) {
-  window_ = NULL;
+  if (window_) {
+    window_->RemoveObserver(this);
+    window_ = NULL;
+  }
 }
 
 void PanelView::OnWidgetActivationChanged(views::Widget* widget, bool active) {