RenderWidgetHostView: Fix a crash that occurrs when the TabContents is being

content/browser/renderer_host/render_widget_host_view_win.cc

Index: content/browser/renderer_host/render_widget_host_view_win.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_win.cc b/content/browser/renderer_host/render_widget_host_view_win.cc
index 21bae6ca6d487098015c1e9d2234781ac7989818..ade9a9f7c352a43361afbb5b531a9e9298c9160a 100644
--- a/content/browser/renderer_host/render_widget_host_view_win.cc
+++ b/content/browser/renderer_host/render_widget_host_view_win.cc
@@ -331,7 +331,11 @@ void RenderWidgetHostViewWin::DidBecomeSelected() {
     tab_switch_paint_time_ = TimeTicks::Now();
   is_hidden_ = false;
   EnsureTooltip();
-  render_widget_host_->WasRestored();
+
+  // |render_widget_host_| may be NULL if the TabContents is in the process of
+  // closing.
+  if (render_widget_host_)
+    render_widget_host_->WasRestored();
 }
 
 void RenderWidgetHostViewWin::WasHidden() {