Move renderFallbackContent() into FrameOwner interface.

Source/core/frame/FrameOwner.h

Index: Source/core/frame/FrameOwner.h
diff --git a/Source/core/frame/FrameOwner.h b/Source/core/frame/FrameOwner.h
index 468acbaf7176a0a0178c324c57d389d5631344ee..5b7f80d36fc9bae52cdbfe60cb62c7a0db052d9a 100644
--- a/Source/core/frame/FrameOwner.h
+++ b/Source/core/frame/FrameOwner.h
@@ -23,6 +23,10 @@ public:
 
     virtual SandboxFlags sandboxFlags() const = 0;
     virtual void dispatchLoad() = 0;
+
+    // On load failure, a frame can ask its owner to render fallback content
+    // which replaces the frame contents.
+    virtual void renderFallbackContent() = 0;
 };
 
 } // namespace blink