Prevent renderer initiated back navigation to cancel a browser one.

Renderer initiated back/forward navigations must not be able to cancel ongoing
browser initiated navigation if they are not user initiated.

Note: 'normal' renderer initiated navigation uses the
FrameHost::BeginNavigation() path. A code similar to this patch is done
in NavigatorImpl::OnBeginNavigation().

Test:
-----

Added: NavigationBrowserTest.
 * HistoryBackInBeforeUnload
 * HistoryBackInBeforeUnloadAfterSetTimeout
 * HistoryBackCancelPendingNavigationNoUserGesture
 * HistoryBackCancelPendingNavigationUserGesture

Fixed:
 * (WPT) .../the-history-interface/traverse_the_history_2.html
 * (WPT) .../the-history-interface/traverse_the_history_3.html
 * (WPT) .../the-history-interface/traverse_the_history_4.html
 * (WPT) .../the-history-interface/traverse_the_history_5.html

Bug: 879965
Change-Id: I1a9bfaaea1ffc219e6c32f6e676b660e746c578c
Reviewed-on: https://chromium-review.googlesource.com/1209744
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Mustaq Ahmed <mustaq@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592823}
void RenderViewImpl::UpdatePreferredSize() {
  if (!send_preferred_size_changes_ || !webview())
    return;

  if (!needs_preferred_size_update_)
    return;
  needs_preferred_size_update_ = false;

  blink::WebSize tmp_size = webview()->ContentsPreferredMinimumSize();
  blink::WebRect tmp_rect(0, 0, tmp_size.width, tmp_size.height);
  WidgetClient()->ConvertViewportToWindow(&tmp_rect);
  gfx::Size size(tmp_rect.width, tmp_rect.height);
  if (size == preferred_size_)
    return;

  preferred_size_ = size;
  Send(new ViewHostMsg_DidContentsPreferredSizeChange(GetRoutingID(),
                                                      preferred_size_));
}

void RenderViewImpl::UpdatePreferredSize() {
  if (!send_preferred_size_changes_ || !webview())
    return;

  if (!needs_preferred_size_update_)
    return;
  needs_preferred_size_update_ = false;

  blink::WebSize tmp_size = webview()->ContentsPreferredMinimumSize();
  blink::WebRect tmp_rect(0, 0, tmp_size.width, tmp_size.height);
  WidgetClient()->ConvertViewportToWindow(&tmp_rect);
  gfx::Size size(tmp_rect.width, tmp_rect.height);
  if (size == preferred_size_)
    return;

  preferred_size_ = size;
  Send(new ViewHostMsg_DidContentsPreferredSizeChange(GetRoutingID(),
                                                      preferred_size_));
}
