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 5045 matching lines @@
   pending_navigation_params_.reset(new NavigationParams(
       common_params, StartNavigationParams(), request_params));
 
   // Send the provisional load failure.
   blink::WebURLError error =
       CreateWebURLError(common_params.url, has_stale_copy_in_cache, error_code);
   WebURLRequest failed_request = CreateURLRequestForNavigation(
       common_params, std::unique_ptr<StreamOverrideParameters>(),
       frame_->isViewSourceModeEnabled());
 
+  // On load failure, a frame can ask its owner to render fallback content.
+  // If it is possible, then there is no more need to load an error page.
+  if (frame_->canRenderFallbackContent()) {
+    frame_->loadFailed();
+    browser_side_navigation_pending_ = false;
+    return;
+  }
+
   if (!ShouldDisplayErrorPageForFailedLoad(error_code, common_params.url)) {
     // The browser expects this frame to be loading an error page. Inform it
     // that the load stopped.
     Send(new FrameHostMsg_DidStopLoading(routing_id_));
     browser_side_navigation_pending_ = false;
     return;
   }
 
   // Make sure errors are not shown in view source mode.
   frame_->enableViewSourceMode(false);
@@ skipping 1520 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