[Panels] Fix browser crash when killing extension on Windows.

chrome/browser/ui/panels/panel_view.h

Index: chrome/browser/ui/panels/panel_view.h
diff --git a/chrome/browser/ui/panels/panel_view.h b/chrome/browser/ui/panels/panel_view.h
index f1019653a6ea26d0174c5bc89a15cb5a26d11207..ae4f5a76a0bf6d8fe140a0e87d6f6cf17cb2e130 100644
--- a/chrome/browser/ui/panels/panel_view.h
+++ b/chrome/browser/ui/panels/panel_view.h
@@ -150,10 +150,12 @@ class PanelView : public NativePanel,
   scoped_ptr<Panel> panel_;
   gfx::Rect bounds_;
 
-  // The window that holds all panel views.
+  // The window that holds all panel views. Lifetime managed by native widget.
+  // See widget.h.
   views::Widget* window_;
 
-  // The view hosting the web contents.
+  // The view hosting the web contents. Will be destroyed when child views
+  // of this class are destroyed.
   views::WebView* web_view_;
 
   // True if the panel should always stay on top of other windows.