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 WebContentsImpl::ResizeDueToAutoResize(
    RenderWidgetHostImpl* render_widget_host,
    const gfx::Size& new_size) {
  if (render_widget_host != GetRenderViewHost()->GetWidget())
    return;

  auto_resize_size_ = new_size;

  for (FrameTreeNode* node : frame_tree_.Nodes()) {
    if (node->current_frame_host()->is_local_root()) {
      RenderWidgetHostImpl* host =
          node->current_frame_host()->GetRenderWidgetHost();
      if (host != render_widget_host)
        host->SynchronizeVisualProperties();
    }
  }

  if (delegate_)
    delegate_->ResizeDueToAutoResize(this, new_size);
}

void WebContentsImpl::ResizeDueToAutoResize(
    RenderWidgetHostImpl* render_widget_host,
    const gfx::Size& new_size) {
  if (render_widget_host != GetRenderViewHost()->GetWidget())
    return;

  auto_resize_size_ = new_size;

  for (FrameTreeNode* node : frame_tree_.Nodes()) {
    if (node->current_frame_host()->is_local_root()) {
      RenderWidgetHostImpl* host =
          node->current_frame_host()->GetRenderWidgetHost();
      if (host != render_widget_host)
        host->SynchronizeVisualProperties();
    }
  }

  if (delegate_)
    delegate_->ResizeDueToAutoResize(this, new_size);
}
