Revert "[OOPIF] Add debugging checks for IPC races between view and frame close."

This reverts commit 96ed9b3f.

Reason for revert: Theory verified. Reverting.

Original change's description:
> [OOPIF] Add debugging checks for IPC races between view and frame close.
> 
> It's unclear how this is happening: one possibility is there's a race
> between WebWidget::Close() actually being invoked in the renderer (it is
> currently triggered via a non-nestable posted task) and the browser
> state being torn down (which sends FrameMsg_Delete from the destructor
> of RenderFrameHostImpl).
> 
> Bug: 838348
> Change-Id: If98c4f104a27f39e083f45f6cd335b326a3976e0
> Reviewed-on: https://chromium-review.googlesource.com/1067577
> Reviewed-by: Charlie Reis <creis@chromium.org>
> Commit-Queue: Daniel Cheng <dcheng@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#560383}

TBR=dcheng@chromium.org,creis@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 838348
Change-Id: I624189fca8b6eae76be26fc1e487ec440b2217e2
Reviewed-on: https://chromium-review.googlesource.com/1069917Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560994}

content/renderer/render_frame_impl.cc

@@ -1938,15 +1938,6 @@ void RenderFrameImpl::OnDeleteFrame() {
   // See https://crbug.com/569683 for details.
   in_browser_initiated_detach_ = true;
 
-  bool is_closing = render_view_->closing();
-  base::debug::Alias(&is_closing);
-  // It is an error to tell a main RenderFrame to cleanup itself, unless the
-  // RenderFrame is provisonal. But since WebView::Close() is deferred (see
-  // RenderWidget::OnClose, which posts a non-nestable task for the actual
-  // WebWidget::Close() invocation), perhaps this is happening somehow...
-  if (is_main_frame_ && !frame_->IsProvisional())
-    CHECK(false);
-
   // This will result in a call to RenderFrameImpl::frameDetached, which
   // deletes the object. Do not access |this| after detach.
   frame_->Detach();