Fix nullptr deref in maybeRenderFallbackContent()

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 <set>
 #include "WebCompositionUnderline.h"
 #include "WebFrame.h"
@@ skipping 135 matching lines @@
                         const WebString& mime_type,
                         const WebString& text_encoding,
                         const WebURL& base_url,
                         const WebURL& unreachable_url = WebURL(),
                         bool replace = false,
                         WebFrameLoadType = WebFrameLoadType::kStandard,
                         const WebHistoryItem& = WebHistoryItem(),
                         WebHistoryLoadType = kWebHistoryDifferentDocumentLoad,
                         bool is_client_redirect = false) = 0;
 
-  // On load failure, attempts to make frame's parent rendering fallback content
-  // and stop this frame loading.
-  virtual bool MaybeRenderFallbackContent(const WebURLError&) const = 0;
+  enum FallbackContentResult {
+    // An error page should be shown instead of fallback.
+    NoFallbackContent,
+    // Something else committed, no fallback content or error page needed.
+    NoLoadInProgress,
+    // Fallback content rendered, no error page needed.
+    FallbackRendered
+  };
+  // On load failure, attempts to make frame's parent render fallback content.
+  virtual FallbackContentResult MaybeRenderFallbackContent(
+      const WebURLError&) const = 0;
 
   // Called when a navigation is blocked because a Content Security Policy (CSP)
   // is infringed.
   virtual void ReportContentSecurityPolicyViolation(
       const blink::WebContentSecurityPolicyViolation&) = 0;
 
   // Navigation State -------------------------------------------------------
 
   // Returns true if the current frame's load event has not completed.
   virtual bool IsLoading() const = 0;
@@ skipping 368 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