[Offline Pages] Add a GCMAppHandler for offline page prefetch.

components/ntp_snippets/content_suggestions_service.h

Index: components/ntp_snippets/content_suggestions_service.h
diff --git a/components/ntp_snippets/content_suggestions_service.h b/components/ntp_snippets/content_suggestions_service.h
index ddd84571739c3390b1d0fdca02e31b32398f14b8..308e4dbe69dca01d8e96b199f6fe4b5fdccc7b5c 100644
--- a/components/ntp_snippets/content_suggestions_service.h
+++ b/components/ntp_snippets/content_suggestions_service.h
@@ -15,7 +15,6 @@
 #include "base/observer_list.h"
 #include "base/optional.h"
 #include "base/scoped_observer.h"
-#include "base/supports_user_data.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "base/time/time.h"
 #include "components/history/core/browser/history_service.h"
@@ -48,7 +47,6 @@ class RemoteSuggestionsProvider;
 // Retrieves suggestions from a number of ContentSuggestionsProviders and serves
 // them grouped into categories. There can be at most one provider per category.
 class ContentSuggestionsService : public KeyedService,
-                                  public base::SupportsUserData,
                                   public ContentSuggestionsProvider::Observer,
                                   public SigninManagerBase::Observer,
                                   public history::HistoryServiceObserver {