PlzNavigate: Allow frames to fallback to alternative content.

third_party/WebKit/public/web/WebLocalFrame.h

 // Copyright 2014 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.
 
 #ifndef WebLocalFrame_h
 #define WebLocalFrame_h
 
 #include "WebCompositionUnderline.h"
 #include "WebFrame.h"
 #include "WebFrameLoadType.h"
@@ skipping 105 matching lines @@
                         const WebString& mimeType,
                         const WebString& textEncoding,
                         const WebURL& baseURL,
                         const WebURL& unreachableURL = WebURL(),
                         bool replace = false,
                         WebFrameLoadType = WebFrameLoadType::Standard,
                         const WebHistoryItem& = WebHistoryItem(),
                         WebHistoryLoadType = WebHistoryDifferentDocumentLoad,
                         bool isClientRedirect = false) = 0;
 
+  // Check if the frame's parent can render fallback content on load failure.
+  virtual bool canRenderFallbackContent() const = 0;
+
+  // Allow the embedders to report that a navigation they handle has failed. The
+  // frame's parent will display fallback content, if possible.
+  virtual void loadFailed() = 0;
+
   // Navigation State -------------------------------------------------------
 
   // Returns true if the current frame's load event has not completed.
   virtual bool isLoading() const = 0;
 
   // Returns true if the current frame is detaching/detached. crbug.com/654654
   virtual bool isFrameDetachedForSpecialOneOffStopTheCrashingHackBug561873()
       const = 0;
 
   // Returns true if there is a pending redirect or location change
@@ skipping 325 matching lines @@
   // to call these on a WebLocalFrame.
   bool isWebLocalFrame() const override = 0;
   WebLocalFrame* toWebLocalFrame() override = 0;
   bool isWebRemoteFrame() const override = 0;
   WebRemoteFrame* toWebRemoteFrame() override = 0;
 };
 
 }  // namespace blink
 
 #endif  // WebLocalFrame_h