overscroll: Show a shadow for the sliding window during nav gesture.

BUG=174219

Review URL: https://codereview.chromium.org/12225163

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@182388 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/web_contents/web_contents_view_aura.h

@@ -27,6 +27,7 @@ class DropTargetEvent;
 
 namespace content {
 class OverscrollNavigationOverlay;
+class ShadowWindow;
 class WebContentsViewDelegate;
 class WebContentsImpl;
 class WebDragDestDelegate;
@@ -172,6 +173,9 @@ class CONTENT_EXPORT WebContentsViewAura
   virtual int OnPerformDrop(const ui::DropTargetEvent& event) OVERRIDE;
 
   scoped_ptr<aura::Window> window_;
+
+  // The window that shows the screenshot of the history page during an
+  // overscroll navigation gesture.
   scoped_ptr<aura::Window> overscroll_window_;
 
   scoped_ptr<WindowObserver> window_observer_;
@@ -193,6 +197,10 @@ class CONTENT_EXPORT WebContentsViewAura
   // pointers.
   void* current_rvh_for_drag_;
 
+  // The container for the content-window. The doc for ShadowWindow explains its
+  // lifetime and ownership.
+  ShadowWindow* content_container_;
+
   bool overscroll_change_brightness_;
 
   // The overscroll gesture currently in progress.