Catch empty PageStates on history navigations earlier.

content/browser/frame_host/navigator_impl.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/frame_host/navigator_impl.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 360 matching lines @@
     // RenderFrameHost as loading.  This ensures that the RenderFrameHost gets
     // in a loading state without emitting a spurious DidStartLoading
     // notification at the FrameTreeNode level (since the FrameTreeNode was
     // already loading). Note that this works both for a transfer to a
     // different RenderFrameHost and in the rare case where the navigation is
     // transferred back to the same RenderFrameHost.
     bool is_transfer = entry.transferred_global_request_id().child_id != -1;
     if (is_transfer)
       dest_render_frame_host->set_is_loading(true);
 
+    // A session history navigation should have been accompanied by state.
+    // TODO(creis): This is known to be failing in UseSubframeNavigationEntries
+    // in https://crbug.com/568703, when the PageState on a FrameNavigationEntry
+    // is unexpectedly empty.  Until the cause is found, keep this as a DCHECK
+    // and load the URL without PageState.
+    if (is_pending_entry && controller_->GetPendingEntryIndex() != -1)
+      DCHECK(frame_entry.page_state().IsValid());
+
     // Navigate in the desired RenderFrameHost.
     // We can skip this step in the rare case that this is a transfer navigation
     // which began in the chosen RenderFrameHost, since the request has already
     // been issued.  In that case, simply resume the response.
     bool is_transfer_to_same =
         is_transfer &&
         entry.transferred_global_request_id().child_id ==
             dest_render_frame_host->GetProcess()->GetID();
     if (!is_transfer_to_same) {
       navigation_data_.reset(new NavigationMetricsData(
@@ skipping 810 matching lines @@
     if (navigation_handle)
       navigation_handle->update_entry_id_for_transfer(entry->GetUniqueID());
 
     controller_->SetPendingEntry(std::move(entry));
     if (delegate_)
       delegate_->NotifyChangedNavigationState(content::INVALIDATE_TYPE_URL);
   }
 }
 
 }  // namespace content