Fix the issue that any tab/window closing hotkey will crash the Pepper Flash Fullscreen.

content/browser/renderer_host/render_widget_host_delegate.h

Index: content/browser/renderer_host/render_widget_host_delegate.h
diff --git a/content/browser/renderer_host/render_widget_host_delegate.h b/content/browser/renderer_host/render_widget_host_delegate.h
index 4f0243ba89f67df471e4a8ea4b74861fe0cc5bcd..29011b53950709e3bdb05835879eb10c25edb2f6 100644
--- a/content/browser/renderer_host/render_widget_host_delegate.h
+++ b/content/browser/renderer_host/render_widget_host_delegate.h
@@ -9,6 +9,7 @@
 
 namespace content {
 
+class RenderWidgetHostImpl;
 struct NativeWebKeyboardEvent;
 
 //
@@ -18,6 +19,9 @@ struct NativeWebKeyboardEvent;
 //  of the RenderWidgetHost.
 class CONTENT_EXPORT RenderWidgetHostDelegate {
  public:
+  // The RenderWidgetHost is going to be deleted.
+  virtual void RenderWidgetDeleted(RenderWidgetHostImpl* render_widget_host) {}
+
   // Callback to give the browser a chance to handle the specified keyboard
   // event before sending it to the renderer.
   // Returns true if the |event| was handled. Otherwise, if the |event| would