PlzNavigate: Allow frames to fallback to alternative content.

third_party/WebKit/Source/web/RemoteFrameOwner.h

 // Copyright 2015 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 RemoteFrameOwner_h
 #define RemoteFrameOwner_h
 
 #include "core/frame/FrameOwner.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "public/web/WebFrameOwnerProperties.h"
@@ skipping 17 matching lines @@
     return new RemoteFrameOwner(flags, frameOwnerProperties);
   }
 
   // FrameOwner overrides:
   void setContentFrame(Frame&) override;
   void clearContentFrame() override;
   SandboxFlags getSandboxFlags() const override { return m_sandboxFlags; }
   void setSandboxFlags(SandboxFlags flags) { m_sandboxFlags = flags; }
   void dispatchLoad() override;
   // TODO(dcheng): Implement.
+  bool canRenderFallbackContent() const override { return false; }
   void renderFallbackContent() override {}
   ScrollbarMode scrollingMode() const override { return m_scrolling; }
   int marginWidth() const override { return m_marginWidth; }
   int marginHeight() const override { return m_marginHeight; }
   bool allowFullscreen() const override { return m_allowFullscreen; }
   AtomicString csp() const override { return m_csp; }
   const WebVector<WebPermissionType>& delegatedPermissions() const override {
     return m_delegatedPermissions;
   }
 
@@ skipping 31 matching lines @@
 
 DEFINE_TYPE_CASTS(RemoteFrameOwner,
                   FrameOwner,
                   owner,
                   owner->isRemote(),
                   owner.isRemote());
 
 }  // namespace blink
 
 #endif  // RemoteFrameOwner_h