PlzNavigate: Allow frames to fallback to alternative content.

content/renderer/render_frame_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/renderer/render_frame_impl.h"
 
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 5052 matching lines @@
   // Also replace the current history entry if the browser asked for it
   // specifically.
   // TODO(clamy): see if initial commits in subframes should be handled
   // separately.
   bool replace = is_reload || common_params.url == GetLoadingUrl() ||
                  common_params.should_replace_current_entry;
   std::unique_ptr<HistoryEntry> history_entry;
   if (request_params.page_state.IsValid())
     history_entry = PageStateToHistoryEntry(request_params.page_state);
   LoadNavigationErrorPage(failed_request, error, replace, history_entry.get());
+
+  // On load failure, a frame may render fallback content which replaces the
+  // navigation error page.
+  frame_->didFailNavigation();

[clamy, 2016/10/21 16:09:42]

I'm a bit worried about how this interacts with the navigation history. In
particular do we create/update the FrameNavigationEntry in this particular case?
If we don't create or update any, could there be some url spoof issue?

[nasko, 2016/10/21 17:00:04]

Should we be loading an error page (last statement before this one) and then
replacing it with fallback content?

I think having a more explicit call to Blink, which returns a boolean whether
fallback content was rendered or not is a bit better. This will allow us to
display that or if no fallback, display the error page.

japhet@ and dcheng@ however are much more knowledgeable in this area, so I'd
defer to them.

[Nate Chapin, 2016/10/21 18:53:59]

That seems reasonable to me.

 }
 
 WebNavigationPolicy RenderFrameImpl::decidePolicyForNavigation(
     const NavigationPolicyInfo& info) {
   // A content initiated navigation may have originated from a link-click,
   // script, drag-n-drop operation, etc.
   // info.extraData is only non-null if this is a redirect. Use the extraData
   // initiation information for redirects, and check pending_navigation_params_
   // otherwise.
   bool is_content_initiated =
@@ skipping 1492 matching lines @@
   // event target. Potentially a Pepper plugin will receive the event.
   // In order to tell whether a plugin gets the last mouse event and which it
   // is, we set |pepper_last_mouse_event_target_| to null here. If a plugin gets
   // the event, it will notify us via DidReceiveMouseEvent() and set itself as
   // |pepper_last_mouse_event_target_|.
   pepper_last_mouse_event_target_ = nullptr;
 #endif
 }
 
 }  // namespace content