Remove early out during shutdown from RenderWidget::OnWasShown

The early out comes from initial.commit, but I think it was not needed
even then. We also RemoveRoute for the IPC channel in OnClose() which
means no new IPCs can arrive. Then GetWebWidget() will return null
after the OnClose() is fully handled, so by then there are no IPCs.

RenderViewImpl can also route messages to RenderWidget, which could
violate the above, but OnWasShown is only sent to the RenderWidget's
routing id.

R=avi@chromium.org

Change-Id: I19438c840c916cb09da8a26e265d390558dbca70
Bug: 896836
Reviewed-on: https://chromium-review.googlesource.com/c/1340483Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609006}

content/renderer/render_widget.cc

@@ -810,10 +810,6 @@ void RenderWidget::OnWasShown(base::TimeTicks show_request_timestamp,
   // for a RenderWidget without a main frame.
   CHECK(!is_frozen_);
 
-  // During shutdown we can just ignore this message.
-  if (!GetWebWidget())
-    return;
-
   was_shown_time_ = base::TimeTicks::Now();
   // See OnWasHidden
   SetHidden(false);