Don't allow RenderFrames to be created during WebContents destruction.

content/browser/frame_host/render_frame_host_delegate.h

Index: content/browser/frame_host/render_frame_host_delegate.h
diff --git a/content/browser/frame_host/render_frame_host_delegate.h b/content/browser/frame_host/render_frame_host_delegate.h
index 92f6c2b1f1026187cf600b91cef44bd180fa0e5e..081986b44116e3abf4105484ac082401c7eb6b0f 100644
--- a/content/browser/frame_host/render_frame_host_delegate.h
+++ b/content/browser/frame_host/render_frame_host_delegate.h
@@ -301,6 +301,10 @@ class CONTENT_EXPORT RenderFrameHostDelegate {
   GetJavaRenderFrameHostDelegate();
 #endif
 
+  // Whether the delegate is being destroyed, in which case the RenderFrameHost
+  // should not be asked to create a RenderFrame.
+  virtual bool IsBeingDestroyed() const;
+
  protected:
   virtual ~RenderFrameHostDelegate() {}
 };