Fix issue with pending NavigationEntry being discarded incorrectly

This CL fixes an issue where we would attempt to discard a pending
NavigationEntry when a cross-process navigation to this NavigationEntry
is interrupted by another navigation to the same NavigationEntry.

BUG=760342,797656,796135

Change-Id: I204deff1efd4d572dd2e0b20e492592d48d787d9
Reviewed-on: https://chromium-review.googlesource.com/850877
Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: Camille Lamy <clamy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528611}
void RenderFrameHostManager::DidCreateNavigationRequest(
    NavigationRequest* request) {
  RenderFrameHostImpl* dest_rfh = GetFrameHostForNavigation(*request);
  DCHECK(dest_rfh);
  request->set_associated_site_instance_type(
      dest_rfh == render_frame_host_.get()
          ? NavigationRequest::AssociatedSiteInstanceType::CURRENT
          : NavigationRequest::AssociatedSiteInstanceType::SPECULATIVE);
}

void RenderFrameHostManager::DidCreateNavigationRequest(
    NavigationRequest* request) {
  RenderFrameHostImpl* dest_rfh = GetFrameHostForNavigation(*request);
  DCHECK(dest_rfh);
  request->set_associated_site_instance_type(
      dest_rfh == render_frame_host_.get()
          ? NavigationRequest::AssociatedSiteInstanceType::CURRENT
          : NavigationRequest::AssociatedSiteInstanceType::SPECULATIVE);
}
