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 5053 matching lines @@
       frame_->isViewSourceModeEnabled());
 
   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;
   }
 
+  // On load failure, a frame can ask its owner to render fallback content.
+  // If it is possible, there is no more need to load an error page since it
+  // will not be displayed.
+  if (frame_->canRenderFallbackContent()) {
+    frame_->loadFailed(error);
+    browser_side_navigation_pending_ = false;
+    return;
+  }
+
   // Make sure errors are not shown in view source mode.
   frame_->enableViewSourceMode(false);
 
   // Replace the current history entry in reloads, and loads of the same url.
   // This corresponds to Blink's notion of a standard commit.
   // 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() ||
@@ skipping 1512 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