Remove deleted offline page suggestions from opened NTPs

components/ntp_snippets/content_suggestions_provider.h

 // Copyright 2016 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 COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 46 matching lines @@
     // If |new_status| is any other value, it must match the value that is
     // currently returned from the provider's |GetCategoryStatus(category)|. In
     // case the given |category| is not known yet, the calling |provider| will
     // be registered as its provider. Whenever the status changes to an
     // unavailable status, all suggestions in that category must immediately be
     // removed from all caches and from the UI, but the provider remains
     // registered.
     virtual void OnCategoryStatusChanged(ContentSuggestionsProvider* provider,
                                          Category category,
                                          CategoryStatus new_status) = 0;
+
+    // Called when a suggestion has been invalidated. It will not be provided
+    // through |OnNewSuggestions| anymore, is not supported by
+    // |FetchSuggestionImage| or |DismissSuggestion| anymore, and should
+    // immediately be cleared from the UI and caches. This happens, for example,
+    // when the content that the suggestion refers to is gone.
+    // Note that this event may be fired even if the corresponding |category| is
+    // not currently AVAILABLE, because open UIs may still be showing the
+    // suggestion that is to be removed. This event may also be fired for
+    // |suggestion_id|s that never existed and should be ignored in that case.
+    virtual void OnSuggestionInvalidated(ContentSuggestionsProvider* provider,
+                                         Category category,
+                                         const std::string& suggestion_id) = 0;
   };
 
   virtual ~ContentSuggestionsProvider();
 
   // Returns the categories provided by this provider.
   // When the set of provided categories changes, the Observer is notified
   // through |OnNewSuggestions| or |OnCategoryStatusChanged| for added
   // categories, and through |OnCategoryStatusChanged| with parameter
   // NOT_PROVIDED for removed categories.
   virtual std::vector<Category> GetProvidedCategories() = 0;
@@ skipping 57 matching lines @@
   CategoryFactory* category_factory() const { return category_factory_; }
 
  private:
   Observer* observer_;
   CategoryFactory* category_factory_;
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_